Harry Potter and the Chamber of Secrets
Penelope Clearwater is a Ravenclaw prefect. She is found lying Petrified next to Hermione, her pocket mirror abandoned nearby. Harry realizes that Hermione must have seen Penelope in the library and asked to borrow her mirror to look around corners for the basilisk (without running the risk of looking the basilisk straight in the eye). When Percy hears that Penelope has been Petrified, he looks pale and stunned: they have been dating in secret for much of the school year. When Percy spent the summer sending letters to some unknown person with his new owl, Hermes, it was Penelope who he was sending them to.