She uses the coin to turn Derek into another bimbo.

Before Derek could stop her, Bonnie reached out with the coin and touched his neck with it. "I think you, like, need to see how awesome it is being a blonde, popular girl!"

The coin began to glow once again, and in a few seconds they were both standing in a completely different room. The furniture was expensive, the walls were covered in posters of boy bands and shirtless actors, and the dominant color was a bright pink. Derek fluttered his long eyelashes and looked down to see his new body. It looked a lot like Bonnie's, a curvy teen girl with perfect skin and stylish clothes, with the distinction that her chest looked smaller but her butt felt bigger.

Derek shook her, his head. New memories were appearing again: being born a girl, meeting her best friend Bonnie in kindergarten, blossoming with puberty to become a mega hottie, joining the popular kids, making fun of nerds. Her new life belonged to Jessica Johnson, and it immediately felt appealing to Derek.