गूफ़

Isle is bothered by people's voices, but not by any other sounds, including ringing phones and doorbells.

The teacher tells Ilsa she know that her (Ilsa's) parents were training her to be a medium so that she can talk to the dead. The teacher says her parents taught her to do that as well. In actuality they were being taught to be telepathic so they can communicate with other (living) people without speaking out loud.