A few days ago, I noticed 1 of my 3 chickens had a very dirty vent area. Thought nothing of it as it has been raining a lot and the coop got flooded. She was acting fine. Today, she has low energy, but is walking around; has a very pale comb; is eating; head drawn in; ruffled feathers; tail feathers droopy. After closer inspection of the vent area, very dirty from poo, swollen looking, some black and yellow discharge. It also appears that she has lost some feathers underneath her tail feathers. There is also a bad odor coming from this area as well, it is not very strong, but almost smells "rotten". The other 2 chickens appear and are acting fine. A very tiny amount of white stool noticed on one of the seemingly unaffected chickens. Any suggestions??