She looks him up and down. No magical presence whatsoever, which means he's probably human. So how did he hear about the school? Most likely from friends or family, but then he should be able to get his answers from them.

"You do need an appointment," she says, "but if you don't mind walking and talking, I have a few minutes before my next meeting. What's your name?"

She starts walking as she asks the question, gesturing for him to come with her. They leave the cafeteria and enter the school hallways, heading for her office. At no point will she be alone with this stranger since the corridors are busy, so she isn't too worried about any nefarious agenda.