I've had this happen before. I always do that, trying so hard to turn them to the good side. Ummm, maybe try to get her back into that kind girl stage and tell her about the mean things they do, or tell her that they will just use her and throw her away like a tissue. Yeah, and keep inviting her to your house, become really close, and when you are so close, like sisters, tell her to drop the group. Idk, I could never get them back after this.