O.K. I am going against what everyone else says, but I "was that girl" at one time, and I disagree - I would leave her alone.
Honestly, I didn't like my mom at that age, and I didn't feel like she was ever supportive of me, so I felt like she didn't need to be a part of my victories or my defeats. Whether or not she realized it, she was very critical, and I figured she didn't need to part of my hobbies and interests.
She did what you all recommend, and continued to go, and I began refusing to compete. I wish she had just left me alone.
I am now about 20+ years past this, and I still wish I would not have refused to compete, but it seemed to be the only way to get her to stop coming. My coach finally made her leave. It was one of the only things I enjoyed (at that time in my life), and I gave it up to prove a point.
Now, we are very, very good friends, but I still believe she could have eased my discomfort and anger if she had just left me alone when I needed it.
I recommend you ask her why she doesn't want you to attend. You explain why you want to attend. If she still is adamant, leave her alone. This, too, shall pass.