About 2 months ago, we adopted a 6 month old female Tuxedo cat from a shelter. She was spayed the day she came home with us. Since the 3rd day home, she has been biting, very, very hard. Enough to draw blood. Sometimes, I can't get her to stop, she will just keep attacking. Other times she is very lovable. She bites if I try to move her off my chair or try to pick her up, but not always. At night she sleeps in the spare room, with a cozy bed and the TV on. If I put her in there and make a move towards the door, she immediately attacks me. She knows I am leaving her. I just don't know how to make her stop. I have tried being stern and hissing at her. I have tried screeching when she bites. Nothing makes her stop, she is not fazed at all. Any suggestions? I am very frustrated. Luckily, she does not do this to the dog, she only play bites her, nothing vicious.