|Berserk! (Circus of Terror) (1968) [Angela Rivers]: Electrocuted by being struck by lightning. (Thanks to Rodzilla)
Twinsanity (Goodbye Gemini) (1970) [Jacki]: Strangled by her brother (Martin Potter), who then cradles her body in his arms as he commits suicide by turning on the gas in the apartment.
10 Rillington Place (1971) [Beryl Evans]: Strangled by Richard Attenborough after being anesthetized into unconsciousness. (We only see a close-up of Richard tightening the cord during the murder.) Her body is shown afterwards when Richard blackmails her husband (John Hurt) into helping him get rid of her body.
Space: 1999: Another Time, Another Place (1979) [Regina Kesslann]: Dies (off-screen), though I don't know any other details. (Thanks to Casey)
Horror Planet (Inseminoid) (1981) [Sandy]: It's been a long time since I've seen this, so I don't remember the details, but I do remember that she (and just about everyone else) died in this movie.