I think the last scene in the The Godfather Part II Fredo's wife is in is after the shooting of Michael's bedroom -- I think she is being forced back to her quarters iirc. It is clear that things are not working out between Fredo and her and that they got divorced soon after the night of the celebration. In any case, we neither see nor hear about her iirc after the shooting. Do we know what became of her?
I am not even sure she was a character in the original book although I know in books written after Puzo he is a major character -- is she discussed and is her eventual fate mentioned?