I understand your loyalty to your friends, but if she said she was sorry might she deserve another chance to be nice to you all? I'm not saying it will be forever either if she continues acting the way she has with you or anyone else then you'll know she didn't change and you can go back to what you're doing now. I just think that giving her a chance might be the right thing to do, and it will make you look good too.
Let me know what you think.