well, i think their behaviour is disgusting.
One could eventually understand that maybe, they want to give oportunity to non-professional to be on stage, and not necessarly "use" the more talented who are already professional or already have experience. but it can still be discussed. Anyway, from what you say, it seems like they are rude with your dd, and i was quite shocked to read that they tried to get her rid of her belt (?!). I can only see jealousy in that! disgusting, disgusting.
I hope your dd will manage to get something this year (as it's the last one if i got it right), but i guess she doesn't need high school theatre to proove (proof) anything. though high school is something else, there are the friends and all...(why not invite her friends to see her outside school performances if she can't perform at school)
i start my senior year too, and everytime i read about high school musicals, i think it's a PITY that we, in France, don't have this AT ALL.