What do I do for a bunny that MIGHT be pregnant?

You should offer her a real rabbit nest box, if possible. You can find them in feed stores like the Tractor Supply Store. Fill it with hay, make a depression in the hay with your fist, and offer her more loose hay to build a nest with, if she decides she's going to. A towel isn't a good idea. Shortly before the birth, she'll carry hay around in her mouth (often a sign of labor and impending birth). Please see my breeding page for more help and good luck with your new bunnies.