How can I NICELY say I don't wanna hang out?

Okay well I'm going into 6th grade and this girl is going into 4th. We used to hang out a lot but I'm going into middle school! I really want a change to make NEW FRIENDS. She's also kinda mean and bratty. She also acts like she's 15 or something! What are some excuses to use so I don't have to hang out with her? She has this idea that I want to hang out EVERYDAY. Help :( ?