That’s weird as I have had a very similar experience!
What I did was just ignore her and hang out with my other best mates, and when ever she wants to talk to/work with me, I just say no and go with someone else!
This girl you are talking about sounds like a waste of time, so don’t bother with her.
She obviously doesn’t care much about you anymore, so act the same way about her, and if she doesn’t go away, speak with your mates/older siblings and they should help you out. :)