This Book Kills by Ravena Guron
Jess is going to school at a posh English boarding school, with super rich kids. She is not one of them though and has never felt like she belongs. Luckily, her friend Clem took her under her wing right at the beginning when Jess first arrived, so at least she has one friend. But when Clem's boyfriend is found dead in the woods around the school, and Jess wrote a short story that basically laid out how the boyfriend was killed, things gets really serious, really fast.
Recommended for grades 8 and up.