I think that is a good idea to put her back, and watch her closely, to make sure that no one is picking her feathers or bullying her. If she has been out of the flock for more than a couple of days, they may pick on her. Let us know how she gets along.
Hens with ascites may have the yellow urates in the droppings, as in this BYC picture below. Seeing poop pictures may help. Is her crop emptying overnight as it should do normally? It seems she is missing a lot of feathers here and there. That can make them look like a hen with water belly. Here...
Is your hen laying eggs? Can you post any pictures of her usual poops? Do the normally white urates in her poop look yellow? Could she be getting feather picked by the others? Have you ruled out any mites or lice on her skin?