Gardner received her MD from Harvard Medical School. She completed a residency in neurology and a clinical fellowship in behavioral neurology at UCSF, followed by a postdoctoral fellowship in dementia epidemiology at the San Francisco VA Medical Center (SFVAMC) and a certificate program in advanced training in clinical research methods and biostatistics at the UCSF Clinical and Translational Science Institute. She is also faculty in the UCSF/SFVAMC Center for Population Brain Health and leads the geriatric TBI interest group as part of the TBI Endpoints Development (TED) initiative. For her clinical practice, she is a staff physician at the SFVAMC where she evaluates and treats military veterans with cognitive and behavioral disorders.