I have 6 cats. I had two Siamese brothers for a year, then got a little female rescue cat.The boys adopted the female as their sister and all was bliss. A year later, I adopted anursing mother cat of eight months old and her two daughters. The mother nursed thekittens on my bed. After she weaned them, I hoped all my cats would get along. Butthe mother and daughters bully the little female who had been here for more than a year,wait for her outside the litter box room (3 boxes), chase her, etc. She is quite frightened,thin, and will eat best when I take her in my room alone, with door closed. She has responded very well to this special attention. But I wonder if I should consider re-homingthe mama-and-daughters? I don't want to do this if not necessary. There are no bigfights, just staring and chasing. The boy cats get along pretty well with the mama-and-kittens, although I can see they aren't fond of them. So far no litter box problems orurinating outside the box.
When females do not get along it can be a very difficult problem to resolve. What you have done is exactly right, give the victim a small place of her own. Food., water, bed, litterbox and your attention when possible. She will be much happier there even though it seems to you like she is alone and isolated.
If you decide to keep the new cats you could put them away at times (not in the victim's room) so the victim can be out with the boys and you again.
Finding them another home is certainly an option as well, but that has to be your decision.
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