How do i befriend a friend?

So i don't want to be friends with this girl anymore. I have a lot of friends and i sit with them at lunch. But she comes over and sits with us too. Every one thinks that she is creepy. But she is in my homeroom so its not like i can avoid her. But i have been distancing myself from her. And now she is asking why i don't talk to her anymore. It's not that i want to become popular i am just losing more of my friends because she is always with me. And i enjoy being around my other friends more than being around her. So how can i tell her to leave me alone and stop following me?