Ultimately if she doesn't want to do it, she will not be happy. However, sometimes children can make brash decisions.
When my daughter was that age she tended to focus on her sport of choice as often as possible. She played and practiced softball all summer and into the fall. By October she would tell us that basketball was her favorite sport. She played and practiced all winter and into the early spring. By March she would tell us that softball was her favorite sport. It was that way for 3 or 4 years until she finally decided to give up basketball and focus on softball. In hindsight we probably could have provided more of a balance between both sports, but we allowed her to pick what she wanted to do. The result was that she would work so much that she got tired of it and switched to the other sport for a few months and then switched back.
When my daughter was that age she tended to focus on her sport of choice as often as possible. She played and practiced softball all summer and into the fall. By October she would tell us that basketball was her favorite sport. She played and practiced all winter and into the early spring. By March she would tell us that softball was her favorite sport. It was that way for 3 or 4 years until she finally decided to give up basketball and focus on softball. In hindsight we probably could have provided more of a balance between both sports, but we allowed her to pick what she wanted to do. The result was that she would work so much that she got tired of it and switched to the other sport for a few months and then switched back.