Help with a stalker???

So there's this girl that is on my track team. I talked to her briefly a few times when my friend was gone from practice, but now suddenly she thinks she's in with my bff' and me! Seriously, she follows my bff and i everywhere silently! She even ed into a private conversation between my bff and her bf!!! She is sooooo creeping me out. And today, we ditched her and hid behind a table in my bff's homeroom, but five minutes later she shows up next to us silently. I don't want to be mean, but I want her to leave me alone!!!! I don't want her to think she's in with all my friends, and I don't really want to be her friend. So how do i get rid of her without being mean?!