This very brief peek from The Owl and the Pussycat (1970) was the only time she clearly bared her breasts on film, and I have never seen the scene in any quality better than VHS (enlargement below).
The film is available free on Amazon Prime right now, so I watched it for a few minutes. The brief topless flash has been snipped out, as it has been in so many earlier versions.
She came very close to nudity in a sex scene in A Star is Born (1976), but the film’s editor always managed to cut away just as her nipple started to appear. (I assume that was to comply with her contract.)