My female and male cats are litter mates, and they used to be a bonded pair- cannot say they still are as of now. After I had gotten both of them fixed, the female gets provoked at little things such as the male going up to her to play. She hisses and growls at the male if he tries play fighting with her, and sometimes even swipes at him with her claws out. The female cat is extremely territorial as well. They are both around a year old, and vet says they are healthy. I have tried reintroducing them to each other, but the behavior persists. What should I do?