|Romeo and Juliet (Giulietta e Romeo) (1964) [Juliet]: Commits suicide by stabbing herself. (I haven't seen this version, but we all know the story...)
For a Few Dollars More (Per qualche dollaro in piu) (1965) [Mortimer's Sister]: Commits suicide by shooting herself in the side to escape being raped by Gian Maria Volonte.
Deadly Sanctuary (Marquis de Sade: Justine; Justine & Juliet) (1969) [Claudine]: Drowned by Mariah Rohm while bathing with her in a pond. We only see the struggle, not the body afterwards. (Nudity alert: Topless & rear)
Cometogether (1971) [Ann]: Reportedly killed in a car crash (along with Tony Anthony and Luciana Paluzzi) when their car goes over a cliff. (I haven't seen this movie myself, and it doesn't seem to be available on video.) (Thanks to Dick Hertz)