Siblings, sister sudden hissing/growling towards brother. Advice please.

[ashleyberner]

It's been one week today that I was woken up by my only two cats who were clearly have a huge disagreement. She was growling, hissing at him from underneath my bed while he was stalking her. I broke it up, and thought that would be the end of it. As siblings, my two have played and wrestled quite often without incident... my boy has played too rough and gotten too hyper at times, and I've had to step in or put him in time out... but they always move on. This did not happen. She would hiss and growl at the mere sight of him the rest of the day. But by the evening, things seemed to calm down. I thought that was it. I slept downstairs to keep an eye on them, because they tend to be active during the night. Everything was okay. Until that afternoon, the same thing... and they ended up in my bedroom with her under the bed and him stalking her.

I called the vet for advice. He said it could be redirected aggression, something I'd never heard of until now. He suggested Feliway wipes and had some samples. I've been using them, but I do not feel they make one bit of difference. It's been a holiday weekend since, so I was unable to inquire about any further options from my vet. My girl continued to be hostile towards her brother even if he was just walking by. I called every one I could think of for advice. Vets, behaviorists. Some had similar advice, some didn't. Most said to keep them separated for a couple of days. So I did, switching them out once a day. My girl spent the night with me in my bedroom, because she is usually the one to sleep with me more than him anyways.

After two days... and as they both kept acting like they were looking for the other, I let them sniff through a crack in the door. It went well. They both seemed calm, so I let them out supervised. We played, had some treats for good behavior, and they both snuggled with me. A cat behaviorist said that when one starts something, they get a time out to diffuse the situation. So that is what I've been doing since. I keep my girl with me in my bedroom in the evenings, and then supervise them during the day. Yesterday went really well, today started a bit rough... but the evening was much calmer. But time outs do seem to give them a chance to cool down. Going upstairs is going to be a hurdle... for some reason she does not approve of him being up there when she is. Makes her nervous. But being on the lower level of the house during the day/early evening supervised is much better.

I'm hoping someone else has been through this and can offer some hope, advice, encouragement. It would be so appreciated. These two are my babies, and I just want them to be happy and calm. There are long moments where they relax, play, and sleep in the same room... which gives me hope that a reconciliation is coming... it just may take a while for her to trust him again, and for him to know to give her space.

UPDATE: When I see the boy attempting to "start something" even though I suspect he only wants to play. I raise my voice at him to stop, back off. And twice tonight he has. When I do that, my girl doesn't panic or run. She sees that he's listening to me. It seems whenever he gets the least bit playful, she hisses at him.