I agree with Blondon704. As tough as it is, she will need to find some way to be more assertive. Going to the teachers can only do so much - little girls can find many ways to be mean and cruel while others aren't looking.
I don't know what you have available where you live, but some sort of self defense class might be a good idea, maybe even take it together. I'm not suggesting violence, but the self-confidence that can be gained by it might do wonders for her.
Sarcasm - just another little service I offer.