There could be various reasons fr this behavior. It could be means of gaining attention or could be just learned behavior. As a parent, always reinstate her good qualities, help her identify the best side of her personality. Meanwhile, look for a counselor around your locality or get in touch with her school counselor. Family therapy would be beneficial in this situation. I know as a mother, you d be extremely worried, just do your best as you already are and dont be disheartened, parenting is tough specially with teenagers. A rrusted adult outside f the family like a counselor could help in restoring the harmony in the parent child relationship.