Dance studio contract

My niece, who is 14 1/2 years old, has grown into a very tall, large-size girl. We have a local dance studio here that has a couple hundred children enrolled, ranging in age from 4 to 18. She has been in their classes & recitals since she was 4 or 5 years old, and has no problem with the dance steps. She is in both tap and ballet. The owner of the dance studio/teacher called her mother and wants to force her out because they feel she is too large to fit in, and the costumes are getting too hard to find. This will devastate this child! Her self-esteem is fragile enough without this embarrassment. Is there anything her mother can do, legally, to keep this from happening? She has always paid the bills on time and paid promptly for any and all costumes, shoes, etc. over the years.

Any advice you can give us will be greatly appreciated.

Thank you
Cathy