That's just it Jim, it isn't rare. It is quite common among young girls and it is getting worse due to society's distorted image of what the female body should look like.

There are warning signs, you just have to watch out for them. If you see something that you don't like, contact your doctor. She is still underage so you can admit her to hospital if necessary. I know this is all worst case scenario stuff, but you're better off thinking about your plan of action if and when the time comes than being surprised.