Drinking could be one of the causes too. A friend went through this with her daughter, started when her periods came on. It was pure hell for her for a few months then she calmed down, stopped drinking cider, she didn't do any drugs. She buckled down, passed her exams and is now one of the most sensible persons you could meet, bright and cheerful and real good company for her mom. It's a phase that some girls go through, so I'm sure your girl will too. Be brave, tough times are worse when it's you alone dealing with the problem.