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Keeleigh Mahler, MSW, LICSW

Keeleigh grew up in rural Michigan on a farm in a large family, where she developed an early appreciation for community, teamwork, and the value of pushing through difficult moments rather than avoiding them. A lifelong athlete with an energetic and deeply relational personality, Keeleigh brings warmth, humor, authenticity, and a strong sense of connection to her work with adolescents and young adults.

Keeleigh is passionate about helping young people build the confidence to face fear, discomfort, and uncertainty directly. Her clinical approach is grounded in strong therapeutic relationships, genuine human connection, and the belief that meaningful growth happens when young people feel both supported and challenged. Keeleigh is known for her ability to connect quickly and authentically with residents, balancing playfulness and humor with honesty, accountability, and deep care. She believes that trust, relatability, and showing up fully as a real person are essential parts of effective therapeutic work.

Keeleigh especially values the experiential and relationship-based nature of Mountain Valley’s approach, where staff work alongside residents in real time rather than limiting treatment to traditional office-based therapy. She appreciates the opportunity to help young people recognize that anxiety does not have to dictate the direction of their lives and that courage is often built through repeated practice in everyday moments.

One of Keeleigh’s favorite parts of Mountain Valley is the sense of community among the residents themselves. She loves how supportive, encouraging, and invested residents are in one another’s growth and how willing they are to face difficult challenges together. Keeleigh also appreciates the creativity, humor, and individuality the residents bring into the community each day, noting that their energy, insight, and ability to support both peers and staff create a uniquely meaningful environment.

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Isabella Tway

Bella earned her bachelor’s degree in psychology from Sam Houston State University, where she initially focused on neuroscience research studying plant-based phytochemicals and their potential antidepressant effects. Although Bella loved the scientific side of psychology, she found herself increasingly drawn toward direct work with young people and the relational side of helping others heal and grow.

Before joining Mountain Valley, Bella worked in ABA with children and adolescents on the autism spectrum. Through that work, Bella discovered how meaningful it was to support young people as they developed confidence, built new skills, and learned to navigate challenges that once felt overwhelming. Bella’s interest in psychology is also deeply personal. Having experienced the impact that compassionate, effective therapy can have in someone’s life, Bella feels strongly about being the kind of supportive presence that helps others feel understood, less alone, and more hopeful about where they are headed.

Bella was immediately drawn to Mountain Valley’s blend of clinical work, experiential learning, and connection to the outdoors. As someone who loves hiking, fitness, and being active outside, Bella appreciated the idea that growth and healing do not only happen in an office, but also through movement, challenge, community, and engagement with the world. Bella also has a strong interest in working with adolescents struggling with OCD and anxiety-related disorders and hopes to continue pursuing that work in the future.

Outside of work, Bella enjoys hiking, strength training, pickleball, and spending time outdoors with her dog, Gemini. A former Division I athlete, Bella played soccer competitively for 17 years. Moving to NH from Texas, Bella is excited to experience life in New England and explore activities that were not exactly part of everyday life back home, especially skiing, skating, and winter in general.

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Katharine Call, MSW

Katharine holds a Bachelor’s degree in Psychology from Dartmouth College and a Master’s degree in Clinical Social Work from Columbia University. Her education allowed her to gain extensive clinical experience in the Upper Valley community, including roles at a local hospital and as an advocate supporting survivors of domestic violence.

Katharine has worked with adolescents and children in various settings prior to joining Mountain Valley. Her experience includes involvement with the mountain biking mentorship non-profit Little Bellas and the local cross-country ski team Ford Sayre.

During her college years and beyond, Katharine dedicated a significant portion of her time to cross-country ski racing, competing professionally for the U.S. Ski Team for several years. Her combined background in professional sports and clinical social work led her to Mountain Valley, where she is passionate about integrating adventure, outdoor activities, and experiential treatments for individuals facing mental health challenges.

In her free time, Katharine enjoys mountain biking, trail running, and exploring the natural beauty of the Upper Valley.

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Miranda Collins, MSW

Miranda has a passion for helping individuals navigate life’s challenges and create meaningful change through a compassionate, strengths-based approach. Her academic and professional experiences have prepared her to support a wide range of emotional and mental health needs with both empathy and practical tools. She believes deeply in meeting clients where they are and walking alongside them as they develop insight, build skills, and grow more confident in themselves.

Clinically, Miranda has worked in both community mental health and public school settings, where she supported children, adolescents, and adults experiencing concerns such as anxiety, depression, trauma, life transitions, and relationship issues. She has a particular passion for working with adolescents and finds fulfillment in helping young people make sense of their emotions, strengthen their coping strategies, and feel more at home in themselves. Her approach is warm, collaborative, and grounded in trust and mutual respect.

At Mountain Valley, Miranda works closely with each resident and their support team to provide care that is individualized, thoughtful, and responsive. She brings a steady and calming presence to her work and values honesty, curiosity, and connection as core parts of the therapeutic process.

Outside of her professional work, Miranda enjoys reading, building Legos, fishing, and spending quality time with her family. These activities help her stay grounded and reflect her belief in the importance of creativity, play, and meaningful relationships—values that guide both her personal life and her clinical work.

MOVING MOUNTAINS

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Landon DuMar, MEd, LMHC, CMPC

At their core, Landon believes deeply in the therapeutic value of play. While growing up, they played sports and personally experienced the suffering that can come from performance anxiety, which became a barrier to finding fun, joy, and play in their life. They distinctly remember the ride home with their team after a soccer game during their senior year, crying and feeling completely alone. In that moment, they decided to quit the sport they had loved and played since they were four years old because they felt so stuck and had no idea how to escape their suffering.

In college, Landon reconnected with their love of play through Brazilian Jiu Jitsu and made the choice to no longer let anxiety keep them from the things they loved. They began learning about the mental and emotional sides of performance and were hooked. They had finally found the practices that helped cultivate freedom from the things that had ensnared their life. They went on to study sport psychology, positive psychology, mindfulness, and counseling while practicing these skills in their own life and sport. This journey of self-discovery ultimately led them to become a therapist, helping others on their own journeys of healing.

Landon has more than ten years of experience working in youth and young adult mental health across residential, wilderness, hospital, educational, athletic, and community-based settings. They are excited to be part of the Mountain Valley community, where they can bring their own unique style and personality to support residents in doing the same.

As an experiential therapist, Landon combines traditional talk therapy with experiential modalities such as games, sports, adventure, movement, expressive and creative arts, mindfulness, animals, nature, and exposure work, helping residents integrate treatment into all aspects of their lives. Through years of working with young people, they have found that creative and personalized approaches that foster love, fun, play, adventure, and creativity help residents become more engaged and connected in treatment, allowing those same qualities to re-emerge in their everyday lives.

In their free time, Landon enjoys spending time in nature, practicing yoga, reading sci-fi and fantasy, Brazilian Jiu Jitsu, working out, playing card, board, and tabletop role-playing games, and watching all kinds of TV shows and movies. They also love animals and will take a moment in their day to pet any animal they can.

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Renee Horst, MS, OTR/L

Renee brings a wide range of clinical experience to Mountain Valley, having worked across home health, outpatient, inpatient, and skilled nursing settings with individuals from infancy through older adulthood. Her background has given her a strong appreciation for developmental nuance, sensory attunement, and the importance of hands-on, experiential work.

Renee was drawn to Mountain Valley after discovering the position while preparing to return to New England. As she learned more about the program, she immediately recognized aspects of her own adolescence in the experiences of the young people we serve. Her history of intense anxiety, avoidance, and fear of judgment informs her deep empathy for residents and her belief in their capacity to build skills, confidence, and meaningful change.

Before becoming an occupational therapist, Renee worked in group home settings supporting older adults with complex behavioral histories who required continuous supervision. That early experience shaped her commitment to trauma-informed practice and her appreciation for environments that prioritize safety, structure, and warmth.

Outside of Mountain Valley, Renee loves reading—especially nonfiction—spending time outdoors, taking on home improvement projects, and being with family. She brings steadiness, creativity, and a grounded presence to the OT team and is grateful for the opportunity to support residents as they take brave steps toward growth. Renee lives in Lebanon, New Hampshire, with her husband and son.

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Sharon McCallie-Steller, MS, MHC

Sharon has lived in New England her whole life, most recently in Vermont, where she and her husband raised their four sons. Sharon attended the Massachusetts College of Liberal Arts in North Adams, MA receiving her BA in English Communications. Her career took her on a journey through many roles in various industries while focusing on raising her family. As her family grew older and began to set out on their own, Sharon began to feel the draw to change her career and focus her energy and talents on helping others. As an adult-learner Sharon received her Master of Science degree in Mental Health Counseling from Springfield College.

Sharon initially worked with adolescents in substance abuse treatment and then was an early member of the clinical team at Mountain Valley Treatment Center. For five years she worked extensively with adolescents with all types of Anxiety, OCD, and related disorders using Exposure Response Prevention therapy, Acceptance and Commitment therapy, CBT, and leading the Expressive Arts Therapy program. Much of her work at Mountain Valley included family therapy and parent coaching. Sharon later worked in an assessment program for boys in the foster care system, and most recently she worked as a therapist at a specialized boarding school for students who have struggled in more traditional settings, facing all different types of struggles.

Sharon’s unique combination of personal parenting experience, direct work with adolescents and their families in an assessment setting, residential treatment setting, and in a boarding school setting post-treatment, allows her to bring a special set of skills to her roles, as part of the Transition Planning Team at MVTC and as a Parent Coach and Program Director of the new Mountain Valley Transitions program.

Sharon believes there is a promise of possibility in every young person, no matter the challenges they face. Sharon believes that every parent that has the desire to be the best parent they can be and is capable of learning how to be the parent that their child needs. She has a passion for helping teens and families wade through the many barriers that can get in the way of reaching this possibility; helping them blaze their own path towards finding meaning, purpose and contentedness while discovering and following their passions; getting reconnected, re-engaged, and pulling in the same direction.

Contact Sharon to learn more about Mountain Valley Transitions.