Catherine is a Lexington, KY native and completed her undergraduate degree at Centre College prior to attending medical school at the University of Kentucky. She then completed an Internal Medicine-Pediatric residency at Vanderbilt University Medical Center followed by a year as the first Medicine-Pediatrics chief resident in 2021-2022. Following her chief year, Dr. Deffendall began her combined adult and pediatric Rheumatology fellowship.

During fellowship, she gained an appreciation for quality improvement research and began a Masters in Public Health in 2024 with the goal of improving care for Rheumatology patients. Her clinical interests are in transitions of care, reproductive health in rheumatic diseases, and systemic lupus erythematosus.