So she faints after she hurts herself? Just checking that I got that right. If she was fainting and then hurting herself it could be an iron deficiency, low blood sugar, low blood pressure.

But if she is fainting after she hurts herself then it is psychological. Possibly the sight of blood? As a kid I used to faint at the sight of a needle but I am over it now (still can't look but at least don't faint at the thought) Maybe have a chat to her and ask her any she thinks she is fainting. Or ask the teachers is they saw anything happen before it happened.

Sorry I can't be more help.