Broodies typically do leave the nest to poop, but there are always exceptions (like your hen.)
I would collect fresh bedding and some rags or paper towels, then lift her out and clean it up. Wipe any obvious poop off the eggs, remove the dirty bedding, put in fresh bedding, put the eggs back in. If the hen is hanging around, let her back in at that point. If she is eating, drinking, pooping, or having a dust bath, let her finish that and put herself back in.
If she will let you, you could gently feel her crop each day. If it has food, she got off to eat, and hopefully pooped too. But if she did not eat, she probably did not poop either-- so it might be good to lift her off the nest and sit her by the food. That will hopefully prompt her to eat, drink, and poop. Or you could just let her decide what to do when. She might have decided not to do that again.