Oh by all means if you can take her to the vet, please do that! We aren't vets, we are just experienced or learned this stuff through years of owning chickens. I'm scared that she's so overweight it's taxing her organs.
Try not let her drink any of that water as the last thing she needs right now is salt! I really hope this works! The other folks might be back by then too!
Sometimes one chicken, just like people, can get fat, but I don't think so here. Do you have any calcium pills? I would pop a 400 iu or something around that into her mouth. That will cause contractions, so if she has an egg stuck (egg bound) at least you're nipping that in the bud as she'd...
What does their diet consist of? I first thought she looked like a coccidia stance, or one of the things the others mentioned, then compared and she's huge!