i'm having the same problem! My mom told me to just talk to her about it but i can't. I kind of just learned to accept it but that's also just as hard as talking about it to her. What i've been trying to do is go to other friends and show her that i need some alone time without clearly saying it. Sometimes she follows me but as long as i'm with my other friends she can follow me and be there ! But remember it just shows she/he likes you or doesn't have anybody else even though they can be annoying!
First, you should try understanding your friend's behavior. Then, you should try to encourage your friend to change the annoying behavior through advice. You should be a role model for your friend to change the annoying behavior.