Take the towel out. It's possible if there was anything, she might have it, but if she doesn't have it yet, then you could prevent it by removing the towel.
You could take a plastic bottle, fill it with hot water, wrap it into a pillowcase and tie it shut, so that the snake can't touch the actual bottle. Put that into the tank, and cover the top with a blanket or towel and see if that warms it some. You might have to replace the bottle once or twice during the night.
How cold is it in the house?
Why did your mom put a towel in the tank?