Hi Katie,
I have not personally had an audition for this role myself, but do know a few people who have done.
From what I've been told, you are sometimes asked to perform a monologue based around a given character profile. There has also been an exercise where auditionees individually have to try and scare one of the judges who is sitting on their own. If I remember correctly, there may be some sort of group exercise too, but I'm not 100% on that.
The process may have changed so take this with a pinch of salt, this is just what has been done in previous years, so I'm told.
Hope it helps, and good luck!