I hate my friend's friend?

I disagree with the first person. If N used to be friends with you and saw how the bully treated you, N had no reason to make such good friends with her. She is a bit of a pushover and maybe it's not worth being friends with her. My plan is that you make really good friends with someone else and N will see and realise what your friendship used to be like and she will become jealous. Then if she asks just say you don't like the bully because she is horrible to you and N may be willing to let her go. If it does work you end up with 2 best friends!