Definitely check for mites and lice, but that said, if I lift my broody off of her nest for any reason, she stays squatted and then stumbles a little before she starts walking normally. I think they must get cramped from sitting for so long, so I wouldn't be too worried. Mine also lose color and weight in their combs over the brooding time. They tend to do a partial molt after the chicks hatch and then gradually get color and weight back. I wouldn't get her off the nest, particularly since the due date is coming up, but I would put the food and water within reaching distance.