It took a LONG time before I was able to my cats interact with my roomates cat. When I first moved in with her she hated Zasper so much that we couldn't even have them within sight of each other. They were let out on shifts, in the morning I would lock Zasper in my room and Sasha had run of her room and the living room, then in the afternoon Sasha would get locked up and Zasper would come out, we switched the cats every 5 hours or so. We did this for several months and finally the two were able to be in the same room without wanting to kill each other. Sasha never leared to like Zasper, but she could at least see her without hissing. She would only hiss when Zasper got near her. THen we got Corkscrew and had to deal with it all over again. We've had Corky a year now and it's the same, she's fine as long as Corky doesn't get near her. And he's so scared of her that he tries his best not to get near her. Luckily for some reason she ignores Tibby, she's just decided to pretend that there is no kitten in the house.