Oh, I'm not. There are a number of ways around it. Hypothetically, we could suppose there was a secret passage out of her room besides the door, for example. Such things are normally forbidden, but then, this isn't 'mystery', is it?

[gives him a pointed look]

Another possibility is there could have been a killer, or a person who would become a victim, waiting in her room for her when she entered. In which case, if her door is still sealed, they would still be inside there, with her. --Or her body.

[shrugs]