I watched this obscure 60's movie the other day, which has also been titled The Atomic Brain, narrated by Bradford Dillman, who became a popular character actor in the 70s.
It has this actress in it who was supposed to land a role in the second of the original Star Wars movies, wearing a mask, so you could not really identity her. Another actress shot the same scene for some reason, but I don't think it was clear what woman was included in the final cut. But anyway, the re-release redone the part anyway.
So, she's this old lady who has a guy working in a lab in her house. She basically wants to be reborn in a young female's body as she has aged considerably. She puts out an ad for a maid, so three young ladies answer it and drive to the mansion. Early on however, one of them vanishes. The old woman just lies to the other hired hands and claims she left. Quit her job.
Turns out they killed her, and merged her with the mind of a cat. There's a pretty silly scene where she gets outside and her friend attempts to convince her to come down off something, just to get her eye swiped at. Then later on, the woman betrays the assistant in her lab, one woman gets electrocuted accidentally, and the last woman escapes after the villain becomes reincarnated as the cat. Which made no sense, but okay. LOL.