The friend, Mary Louise Kane said on Wednesday that von Trapp died Tuesday at a hospice in Towson, a suburb near Baltimore. She suffered congestive heart failure in November.
Von Trapp was the oldest daughter of Austrian naval officer Capt. Georg Ritter von Trapp. The captain's seven children were the basis for the singing family in the famed 1965 film.
Kane lived with Agathe von Trapp for five decades and ran a kindergarten with her at the Sacred Heart Catholic parish in Glyndon, Md.
The Associated Press contributed to this report.