谢弹指MM, I have the same concern: 如下：

she seems is on the slim side, she dance 6 year ballet, it helps. we eat organic food, she is a delicate eater.
she is still growing no period yet. she is mid and long distance swimmer , it require 技术和耐力
there is a swimmer‘s mom in our club , she has high school girl's body in her 40's ,three kids. out of my surprise , she was the college swimmer , and first league swimmer, must be national ranking top 25. she still swimming.
真问题： the dancer ,swimmer facing the problem is when they stop to do what they have been doing, it is moment to grow out of good shape. my best friend's daughter is a balletrina , after she quit ballet went to law school, stop dance, she 长了25 磅。
some time those things worried me. I wish she can take sports as a life style , keep doing in the future, not totally stop at any point.