What to do when your friend is being a unreasonable?

my friend is being completely unreasonable saying i am being stupid for wanting to make something work out and she has done the exact thing i am doing. she dropped everything for someone else. rescheduled her b day party for her and everything. i told her my mom said i couldn't do something and she said i was being stupid and making it up...she also cries when i don't do something, like a spur of the moment thing, if I'm not allowed she gets mad at me and calls me a *****. i am always with her and do pretty much whatever to make her happy, but i simply have no one to talk to this about to so i don't know what to do. i don't know how to make her believe me that i am not lying. my parents wont let me! ahhhhhhhhhh.