My first bet was that she came to the school several years after the ritual took place and now investigates Kat's disappearance.
Now I have a second bet - she is one of previous victims of the ritual, who found her way into that creepy mansion (explains the creepy pictures on the walls too) and now lives there alongside with other victims (like hooded person at the picture) because it looks like there is no escape from this hellish place. Just looks like, not really.