She is the youngest of three daughters to Katherine and Ray Wiley, and graduated from Highland Park High School in Dallas, Texas in 1975.
Cassella worked for Prentice Hall Publishing Company in New York City before deciding to attend medical school.
Prior to writing fiction, she wrote medically centered articles for The Bill & Melinda Gates Foundation profiling their grant recipients working in low resource countries around the world.
After completing her internal medicine residency at Virginia Mason Medical Center, Cassella practiced primary care at Pacific Medical Center, SeaMar Community Clinic and Pike Market Community Clinic[permanent dead link], with a special interest in cross-cultural medicine.
[8] Her books have been highlighted as top choices by Library Journal, Booklist, Harpers Bazaar, People Magazine, Poets & Writers, Womans Day, and USA Today.
[citation needed] All of her novels draw from her personal experience as a physician, her role as a mother, and her interest in medical ethics and the complexities of contemporary healthcare.