So good to know that it's not as serious as I feared... My first reaction was impaction (since it's bulging) or some sort of weird hernia (which I guess it sort of almost is?)
I'm going to take the humidifier from my (dearly departed) hermit crabs and set it going for her habitat, on full, to keep things moist. That ought to be sufficient, right? She doesn't ever like to sit in water or bathe and doesn't like to be sprayed. I also definitely don't want to try to wrestle her out of her hiding place right now- unless it's easier in the morning, the whole thing is going to the vet with us tomorrow.
Thank you all- I'll keep you posted.