PLEASE PLEASE ANSWER FAST! How can I finaly stand up to my friend?

[Singer_Star]

I am tired of her pushing me around and giving me bad singing comments when everyone I know besides her sister say she stinks. I mean she is good but she forces it. And well she is always like "But it's my house." or "But i'm the guest." I am tired of it. And if she doesn't get a part she wants in a play remake we do she gets mad and will either not do it or will be like "If I can't be it then you can just go home!" it ticks me off so much! Please answer! I could really use some advice!
The thing is, is that I can't really yell at her cause she will tell her family and everything. I mean she is nice except for when she doesn't get her way. Sometimes she will hit you for not doing this or that and stuff. I don't want to upset her to much cause we have been best friends since I moved to this neighborhood and stuff and he rparents pretty much consider me family and stuff. So please please give me some advice!
Okay to the Fryea S. I did leave when she told me to sometimes and she didn't care. And I do let her be the part cause if I don't she will get mad. So she is ALWAYS the part. I have never gotten to be it more than once. And last time I got to be the part she was mad and started criticizing how I was acting when everyone else thought I was good.