Thanks for your help, we decided to put her down because was suffering and it was just getting worse. She was pretty old and the vet isn't really an option. Now I know to watch for this in the others too so we can catch it before it is too late!
I have a hen (Isa Brown) who has a prolapsed vent. Didn't catch it until this morning, but it must have happened awhile ago but she has very nice vent feathers that must have hid it until it got infected and the other chickens have pecked at it. I think she has pus leaking that is drying on her...