The fact she has spoken to someone about it, looks like a good sign to me. She obviously wants help to sort this out. I'd be more worried if she was refusing to talk about it, so if I were you, I'd talk to her and find out exactly what she wants to happen from this point.

Then devise a plan together about what you can do. It will giver her ownership of her own life, and maybe some empowerment back.

So the goal may be for them to leave her alone, but from hassled daily to being left alone is a big step, so break it down.

From her goal, you would have a plan like:

Talk to the head teacher
Arrange a meeting
Talk to the other parents.

Break it down into small steps, and at least then she won't drown in the bullied to left alone gap.