Ms. Duncan decided that Clare would be kicked out of the prom. James wasn't staying there without her, so he asked for a refund. As Clare and James had come with friends, all of them decided to leave together, and so all of them wanted refunds.
For now, Clare wasn't interested in getting a refund. She didn't see why she had to leave at all. She hadn't put all this effort into her prom night for no reason. She stood her ground.