I wouldn't try to think about this too hard. I had my audition last year and they asked us to do a piece of theatre lasting 30 seconds, no speaking, based on the words "nobody said it would be this easy/nobody said it would be this hard/do do do do do i wanna" Just grab a picture of yourself (possibly a baby pic) and just see what it inspires you to create. I was dreading my audition aswell, but when i got there, they made the room all do it at the same time, then we were partnered up and asked to combine what we had. All in all i think they look more at how you react and work with other people. I had a really fun time at my audition, we played games etc, didn't feel like an interview lol. What you create doesn't have to make sense to others, the teachers just like to see a process.
Jen xx