|Backfire (1950) [Lysa Randolph]: Killed (off-screen) by Dane Clark (though I don't know any other details).
Moonfleet (1955) [Mrs. Minton]: Shot in the chest in the crossfire of a shoot-out between the soldiers and Stewart Granger's band of smugglers on the beach. Shown from a distance.
No Exit (Sinners Go to Hell) (1962) [Inez]: Dies of carbon monoxide poisoning when Susana Mayo turns on the gas stove before going to bed with Viveca, as a murder/suicide. (I haven't seen this film, so I don't know whether their deaths were depicted on-screen or not, but I am familiar with the play, which is set in the afterlife.)
These Are the Damned (The Damned) (1963) [Freya Neilson]: Shot in the back by Alexander Knox after she learns too much about the secret operation on the island. Shown from a distance. (Thanks to Brian)
Cauldron of Blood (El Coleccionista de cadavres; Blind Man's Bluff) (1970) [Tania Badulescu]: Dies of shock after her right arm is plunged into a vat of acid (and dissolved down to the bone) during a struggle with Boris Karloff. (Thanks to Thomas)
The Hand (1981) [Doctor]: Strangled by Michael Caine's disembodied hand (also hitting her head on the floor as she falls over).
Creepshow (1982) [Aunt Bedelia]: Strangled by a zombie in a graveyard. Her body is shown again when Ed Harris falls into an open grave and she falls on top of him.