Update: Well, I'm back from the pond and the results were somwehat inconclusive. She kinda would thrash around and float a little but then she would stop and sink a little then she would thrash and float then pause and sink and on and on.
It was really kind of confusing. Were the evil spirits going in and out, in and out, in and out of her body just to confuse and deceive us? None of us were too sure. After about half an hour she just kinda settled to the bottom and stayed there.
The good news is I guess she wasn't a witch after all. My bad.
