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About Us

Leadership Team

Chief Executive Officer, Dr. Kathleen O’Brien, Ph.D.
301-997-1300 ext 803 

Kathleen O. O’Brien, Ph.D., is CEO of Walden/Sierra, Inc. a premier behavioral health organization serving Southern Maryland. She earned her Bachelor’s and Master’s degrees from the University of Maryland, and her doctorate in Clinical Psychology from LaSalle University.

Dr. O’Brien began her long association with Walden/Sierra in 1973, serving as the Clinical Director from 1978 to 1990, when she became the Executive Director. Her commitment and dedication have been a driving force in the development and expansion of a multi-service behavioral health organization that is respected throughout the State and has received national recognition.  Read More

Chief Operating Officer, Gary Lynch, LCADC

301-997-1300 ext 807

Gary Lynch, MA, LCADC, Chief Operating Officer of Walden/Sierra Inc., is a Licensed Counselor with the Maryland Board of Professional Counselors, a Certified Chemical Dependency Counselor with the Maryland Addictions Professional Certification Board and a Certified Practitioner of Neuro-Linguistic Programming.   Read More


Clinical Services Operator, Elizabeth Lenhart-Cooksey, LCSW-C, LCADC
301-997-1300 ext 805

Betsy has been working in the clinical and administrative aspects of the substance abuse and mental health field since 1994.  She holds a MSW from the University of Maryland School of Social Work and a MA in Counseling Psychology from Bowie State College.  Betsy completed her undergraduate work at Towson State University.  She is a Licensed Certified Social Worker-Clinical (LCSW-C) and a Licensed Certified Alcohol and Drug Counselor (LCADC).

Betsy’s professional experiences include clinical work in private practice and in day treatment programs.  She has also served as the Director of Family Support Services at Hospice of St. Mary’s.  In 1999, Betsy joined the Walden staff as a Clinical Services Coordinator in the substance abuse treatment program.  Since that time, she has held positions of increasing responsibility to include Program Supervisor and Residential Services Coordinator.  Until her promotion to Clinical Services Director in 2011, Betsy had been serving most recently as Walden’s Outpatient Treatment Supervisor with clinical and administrative oversight of Walden’s outpatient sites in Lexington Park, California, Charlotte Hall and Waldorf. 

As Clinical Services Director, Betsy has a unique opportunity to assist adolescents and adults seeking treatment for substance abuse or co-occurring substance abuse and mental health treatment as well as to interact with family members.  She is also actively involved in representing Walden with community partners, to include the St. Mary’s County Detention Center, the Department of Social Services, the Department of Parole and Probation, Medstar/St. Mary’s Hospital, Health Connections, and Greater Baden Medical Services.



Recovery Services Director, Laura Webb, M.A., A.C.E.
301-997-1300 ext 804

Laura directs the free and open to the public services available at Walden's Beacon of Hope Adult and Cove/DFZ  Youth Community Centers focused on wellness and recovery as well as supervises Walden's cadre of peer support staff.  Trained as an adult and community educator and writer, Laura is a certified instructor of Mental Health First Aid, Youth Mental Health First Aid, CCAR Recovery Coach Academy and Risking Connection.