Over time I know I've seen similar posts, but now I'm in the "please, please help!!!" category where I can't find any of the other posts to help, so sorry for repeating.
Squawk, my one year old, usually very healthy hen has just developed this large pouch under her vent (not coming out of the vent, but close). It's very soft and she usually lays an egg a day (she may have today, but I'm not sure), but her whole backside is so sore when I touch it that she practically screams. Freaks out over a warm bath. She's been molting for about a week now, but when this developed, all 19 other birds violently went at her, especially this warm lump.
As far as I can tell, there are no mites or worms. She is very thirsty, and now isolated in our bathtub with drinking water, food and a blanket.
Can't get a local vet to look at her (apparently all are away for the weekend...we live in a small area)