Rachel In The Real World

Rachel complains about how Cassandra July picks on her, but is the only student to question her and contest her will.

She is disrespectful to her dance teacher and practically stalked Carmen Tibideaux when she was rejected.... but is rewarded with an invitation to the winter showcase as if to give the thumbs up to such behaviour.
I don't quite understand why Cassandra July is so rude towards Rachel from the point of meeting her, it seems like pointless and unexplained conflict created by the writers but instead of acting like a polite student, she returns that attitude to her teacher and then claims she's being picked on, not at fault.

I seriously doubt that Rachel Berry would function well in the real world...