Are you talking about "Crazy Joe" (1974), the story of New York gangster "Crazy" Joey Gallo? Because I find no listing at the Internet Movie Data Base of her having been in that.
Okay, just found a listing for "Joe" (1970), with both Boyle and Sarandon.
Regards,
I think she was actually the daughter of the Madison Ave character who killed her boyfriend. But that movie was a looooong time ago.