O'Neill may be best remembered for her role in the 1971 film "Summer of '42", where she played Dorothy Walker, the early-20s wife of an airman who has gone off to fight in World War II. She stated in a 2002 interview that her agent had to fight to even get a reading for the part, since the role had been cast for an "older woman" to a "coming of age" 15-year-old boy, and the director was only considering actresses over the age of thirty, Barbra Streisand being at the top of the list.