Ariella and the Lost Spirit

Receiving her Hogwarts letter was the best thing about Ariella's summer. Now that she's here, it doesn't seem so great. The slytherins are making fun of her accent, and her roommates seem to not like her very much. Ariella finds a spirit that no one else can see while exploring the castle. She tells her that something is wrong with the ghosts. Can Ariella solve the mystery?