She's being so annoying and desperate?

In 6th grade I was like, BEST FRIENDS with this girl, Karlie. But everyone, even my mom, hates Karlie. Even I started to hate Karlie in the summer after 6th grade. She's like a 4 year old trapped in a 13 year old's body. Me and all my friends grew up a lot that summer, but she didn't. We all started shopping at "older" stores, straightening our hair, and wearing makeup, and Karlie got all p***ed at us (ha...Like we cared.) Now she's being all desperate, wearing FULL outfits from PINK, from her shirt to her shoes. She's also trying to wear makeup, but it looks like crap. She always tries to talk to me and all my friends, but they all hate her. Now she's gone to try to pretend to be best friends with the girls from my old school, even this one girl Gabbie, who's been a good friend of mine since before I can remember. Everytime she hears me say "Gabbie", she runs up and says "GABBIE *SMITH?!?!?! I LOVE HER!!!" even though she's met Gabbie once. It's soooo annoying!! How should I deal with this without, i dunno, screaming at her like a maniac??