Having taught Muslim children in the UK in the days when the Hijab was causing problems, I found that most girls actually wanted to wear it. I am aware that this is a bit different but the principle remains the same. I supported my Muslim students then and I would do the same now. If she wants to wear it, then she should be allowed to wear it. her father doesn't seem to be forcing her, he is trying to force the school to allow her to wear it. I would do the same