However, you need to be realistic about your skill level and the others. It is possible that there is a significant difference. You need to speak to your teacher - ask when she is not busy - maybe make a time to ring her or meet her.
She has obviously told you over and over the costume is "modern" - I'd say a cheap way to costume students. Unflattering fo 95% of dancers. This could be her way of trying to get rid of you - certainly I would never impose such an ugly choice on my students.