Harry and Ron had just arrived at the bathroom, looking for Hermione to tell her about the troll. As they reached the door, they heard a shout.
"Buster!"
Suddenly, a giant beam of light shot through the door, carrying the troll with it. It, and the troll, then smashed through several walls. By the time the troll stopped going through walls, it was dead.
Hermione then stood straight and shouted at the troll.
"Don't mess with a student of the White Devil again if you know what's good for you!"
I have no idea where I got this... but a Nanoha trained anyone can't be good for who they fight against.
Stay healthy, stay alive, and stay away from fights with Nanoha in them, it's not conductive to either of those.