Turns out problem was not any kind of internal infection or illness. It was an animal attack. Found the offending critter attacking other chickens. Another hen got it pretty good.
Some pretty nasty wounds. All the magots are cleaned out of the first hen. Externally she's looking much better...
Washed, hydrogen peroxide, washed again, epson salt soak/clean, iodine just pored it all in there. I was expecting the a alien to leap out the back. There were more magots still.
Got yogurt and put apple cider vinegar in the flock's water. There's so many magots. Couldn't have been more than...
Resurecting this thread. I have a hen that defintiely has this problem. I just washed/cleaned out the area, but this ide of injectable antibiotics, doesn't sound like something I pick up at Walgreens. Any ideas for care/cure?