A board-certified veterinary oncologist, Mullin received a VMD from the University of Pennsylvania School of Veterinary Medicine, completed an internship in small animal medicine and surgery, and pursued a 3-year residency in medical oncology. During her residency, she conducted bench top research in osteosarcoma at the Pediatric Oncology Branch of the NIH National Cancer Institute, for which she received the 2014 Most Outstanding Resident Basic Science Research award from the Veterinary Cancer Society. She has authored/coauthored multiple journal articles and book chapters.