请将以下文章中的语法错误找出并改正。
My sister she is going to school is 7 years old. She likes to playing soccer with her friends.
My sister, who is 7 years old, is going to school. She likes playing soccer with her friends. 

Correction: 
- Remove the second "she" after "sister".
- Remove "to" before "playing".
- Add a comma after "old".