She was pissed off at Wayne yes but really in hindsight she over did it. Wayne was paranoid and it bit him in the ass but Cassandra really loved him when it mattered. Bobby was just an obsessed loser who couldn't get it in his head that Cassandra didn't care for him romantically. He was so used to having people bow to him that it blew his mind that she loved and cared for Wayne so much. He was "no good for nothing punk."
He had to resort to the lowest common dominator to get her to marry him by buying off her father and family with the green cards. In hind sight she would have been screwed over; dumped by him and the company once they found someone else. She was smart to leave. It may have ruined things for her but she got a better life as a result.

I saw it more as marrying Bobby on a whim, because she was annoyed at Wayne and impressed at Bobby's skills as a music producer, but snapped out of it.

1. They are parodying "The Graduate".
2. Cassandra sang in the first and got a multi-record contract from Mr. Sharp in the 'mega happy ending'. At the beginning of the second film, she is recording and promoting the first record of that contract.
3. They were playing up the Chinese stereotype of being "traditional" i.e. the father arranges the marriage and the daughter must obey. Jeff(her father) wanted her to marry Bobby despite Wayne being an excellent warrior. lol Which is the ENTIRE reason Wayne is organizing Waynestock(to impress Jeff so he'll be allowed to marry her instead).
   I have learned from experience that a modicum of snuff can be most efficacious.