so if your lising... please help me..

So there is this girl.. And everytime me and her are togethor (JUST US) we have such a great time and were laughing and were like best friends(NOT REALLY) but anyway when im with her and a whole other bunch of people she treats me like dirt... like for example on time me and her and our whole group of friends had a sleepover and i was texting and she got mad cause i was texting my best friend and my boyfriend. then she turned everyone against me. then i got upset and she made it seem like my fault. and i was really upset so i sat on the couch and plugged in my headphones and blasted taylor swift music in my ears since she always makes me feel better and i wouldnt be able to hear anyone else since i was upset. so then she got mad at me for that and made everyone else mad too.   ALSO when its me and her shell talk about people then go and be there best friend. That pisses me off. then i found out she does it to me too... I really want to be friends with this girl but what do i do? so if your listing... please help me..