Help! Gummed up/prolapsed vent 3rd pic. Graphic

[anythingbutsandy]

I've soaked her bum and it got most of the gummy stuff and the stink off. I've applied Preperation H and gently pushed the bulge back up in there, but I don't think it did much good. She's now resting (I hope) in a dog cage/kennel for the night.

She's 1 of 8 red sex-link hens -- should I start worrying about the other 7 now? Is this common?