Whitner is a graduate of Howard University and Howard University School of Law. After admission to the Maryland Bar, Whitner received a direct commission as a first lieutenant to the U.S. Air Force where she rose to the Air Force Court of Criminal Appeals, the highest court of the Air Force. Whitner was honorably discharged from the U.S. Air Force as a captain in 1999.
In 2000, Whitner joined the U.S. Virgin Islands Office of the Attorney General. She also joined the U.S. Virgin Islands Air National Guard, where she again served as the Judge Advocate General for both the U.S. Virgin Islands Air and Army National Guard.