Meet Our Staff

Clinical Staff


Shannon D. Mullen, Ph.D., CSAT

Shannon D. Mullen completed her Ph.D. in Counseling Psychology from The University of Tennessee in Knoxville, Tennessee in 2008. Dr. Mullen is a licensed psychologist in the states of Georgia and Florida. Prior to her doctoral studies, Dr. Mullen completed a Master of Arts in Counseling at the University of New Orleans. Dr. Mullen established Mosaic Psychological Services where she provides clinical and forensic services. Clinical areas of specialty include trauma, attachment, sexual health/addictions, and psychological evaluation. Additionally, as a Certified Sexual Addiction Therapist, Dr. Mullen provides targeted interventions for individuals and couples struggling with sexual infidelity and addiction to sexual material and behaviors. Adolescent and adult patients are helped through the recovery process through the use of specialized interventions to initiate and sustain long-term recovery and restore relationships broken by betrayal trauma. Dr. Mullen has more than 10 years of treatment and assessment experience in sexual disorders and addiction. Treating the whole person is a hallmark of Dr. Mullen’s work and she approaches each person or couple with attention to the physical, emotional, and spiritual dimensions of their personhood. Christian Theology is a welcomed addition to this clinical work and forms the psychodynamic lens through which the whole person is restored to dignity and health. Georgia License PSY003406 & Florida License PY10361

Mandy B. Mullen, LCSW, CPTT Candidate

Mandy B. Mullen is a Licensed Clinical Social Worker in both Georgia and Florida. Ms. Mullen received a B.S. in Human Services and has a Masters of Social Work from Florida Gulf Coast University in Fort Myers, Florida. Her current professional specialities are play therapy, trauma counseling, child and adolescent behavioral problems as well as marital therapy and relationship counseling. Ms. Mullen is currently working on her Certified Partner Trauma Therapist (CPTT) credentials. She is certified in Trauma Focused Cognitive Behavioral Therapy (TF-CBT) and E.M.D.R. Ms. Mullen is also the System of Care Director and is responsible for ensuring the best patient experience for receiving services at Mosaic. Georgia License CSW004523 & Florida License SW10187

David Valpuesta, LMFT

David Valpuesta received his Master's of Science in Marriage and Family Therapy from Valdosta State University. Prior to obtaining his Master's degree, Mr. Valpuesta received his Bachelor of Science in Psychology from Florida State University. As a Marriage and Family Therapist, he understands that when people experience trauma or severe stressors, life may seem to unravel. It is his passion to help couples, families, and individuals experiencing martial or relational conflicts, adolescent behavioral problems, and bereavement issues. Georgia License MFT001440

Rachelle H. Cantin, Ph.D., NCSP

Rachelle Cantin, Ph.D. is a licensed psychologist in the state of Georgia and a Nationally Certified School Psychologist (NCSP). Dr. Cantin obtained her undergraduate degree at Albion College, where she graduated with honors. Dr. Cantin received her Ph.D. in School Psychology from Illinois State University. While at Illinois State, Dr. Cantin was bestowed the Ora Bretall Graduate Fellowship and University Fellowship. She concluded her doctoral studies with a clinical internship at the APA-approved Florida State University Multidisciplinary Center (FSU MDC). Dr. Cantin has completed specialized training in autism spectrum disorder (ASD), anxiety, trauma, and neuropsychological assessment. She has extensive experience in the evaluation and treatment of developmental, educational, and behavioral disorders among child and adolescent populations. Dr. Cantin holds additional certifications as both a Certified Clinical Telemental Health Provider (CTMH) and a Certified Clinical Anxiety Treatment Professional (CCATP). Georgia License PSY003823 & Florida License PY10943

Carrie Milhous, LPC

Carrie Milhous believes that psychotherapy is a process of healing and of discovery that leads to an awareness of who you are and who you were created to be. Her clinical experiences include working with adolescents and adults who live with ADHD, anxiety or affective disorders, assisting parents in developing successful parenting strategies, marriage preparation and enhancement, and supporting older adults as they encounter disabilities and caregiving responsibilities. Carrie favors a strength based approach with a cognitive behavioral orientation and she is also a trauma informed therapist who is an EMDRIA approved EMDR therapist. Carrie is a Licensed Professional Counselor in the State of Georgia. She obtained her Master of Arts degree in Counseling at the University of Notre Dame, and a Certificate of Advanced Graduate Studies in Clinical and Community Counseling from Johns Hopkins University. Prior to that she received her Bachelors of Science in Psychology at Georgia Southern University. Georgia License LPC005462

Kate Harrison, Ph.D.

Dr. Kate Harrison is a licensed psychologist in both Georgia and Florida. She received her doctoral degree in Clinical Psychology from Louisiana State University. Prior to receiving her degree, she completed an American Psychological Association-approved internship at the Florida State University Multidisciplinary Center (FSU MDC), where she had specialized training rotations in the assessment of Attention-Deficit/Hyperactivity Disorder and Autism Spectrum Disorder. She subsequently received postdoctoral supervision and training at both the FSU MDC and at Mosaic Psychological Services, LLC. Dr. Harrison has clinical experience in the assessment and treatment of children and adolescents with neurodevelopmental, academic, behavioral, social, and emotional difficulties. Her professional interests include the assessment of ADHD, learning disorders, and disruptive behavior disorders and the treatment of anxiety, defiance, anger, emotional and behavioral dysregulation, and executive functioning abilities (e.g., time management, organization). Dr. Harrison is passionate about helping children and adolescents improve their overall well-being and achieve their personal goals. Georgia License PSY004169 & Florida License PY10053

Megan A. Nichols, Ph.D.

Dr. Nichols is a licensed psychologist in the states of Florida and Georgia. She specializes in the assessment and treatment of children and adolescents, with a particular interest in Autism Spectrum Disorder. She completed her doctoral studies at Florida State University where she received extensive training in assessment, consultation and intervention across clinic, hospital, school, and university settings. Dr. Nichols earned her B.S. in psychology from the University of Central Florida and was also licensed as a general education and special education teacher in the state of Florida, where she had experience teaching students with Autism Spectrum Disorder in the general education, self-contained, and residential settings. Dr. Nichols joined Mosaic Psychological Services following the completion of an APA-accredited Predoctoral internship and Postdoctoral residency at the Florida State University Multidisciplinary Evaluation and Consulting Center. Her training primarily emphasized the neurodevelopmental assessment of Autism Spectrum Disorder, attention disorders, internalizing concerns, and learning disorders. She also has experience providing consultation, positive behavior support, and mental health services to students in rural school districts, and parent training. Her professional interests include social skills training, improving social-emotional health, and understanding the effects of technology use on children and adolescents. Georgia License PSY004455 & Florida License PY10693

Lauren Santos, M.S.

Lauren Santos graduated from Northwestern University with an M.A. in Clinical Mental Health Counseling in December 2020 (from a Counseling and Related Educational Programs (CACREP)). This program emphasized a psychodynamic approach to counseling that Ms. Santos applies to her counseling approach. She received a B.S. in psychology from Georgia Institute of Technology. Ms. Santos is working with adults, adolescents, and children with depression, anxiety, and trauma-related issues. Currently being supervised by Shannon Mullen, Ph.D.

Office Staff


Stephanie Bufford
Administrative Assistant

Paula Jensen
Intake Coordinator

Ashley Watson
Billing and Credentialing Specialist

Lehana Morrell
Testing Coordinator