I NEED HELP WITH MY ANNOYING FRIEND!!!?

Okay so me and my BFF have been friends since third grade(we're 15 now) and so ever since last summer vacay started, she's been really annoying and kind of immature. SHe calls me CONSTANTLY and thinks that Im on the computer 24/7 just so we cna chat!I'm older than by four months, and she tries to act like she's older and tries to act 'cool' by INSULTING people! It's just that she's gotten on my nerves TOO MUCH lately. I need help, PLZ!!!!! I want to tell her she's annoying me, but she's also oversensitive (a lot of ppl at my school have been thinking about her annoying them, trust me, Im not trying to insult her back). HELP! :(