I'm going to tell my best friend she annoys me
Why would you tell your best friend that?
I just want to tell her she's being annoying
The best policy is to be honest with your friends and if yours is doing something to annoy you, it might be good to let her know. Your friend might not be aware that their actions are annoying, so tell them in a kind and respectful way and hopefully the problem will be solved.
I need to be a bitch and tell my friend she is being annoying even though she is a good friend of mine.
As long as you do it respectfully, that is a good thing to do. She may not be aware and this will allow her to change her behavior.