The update is, she is at the vet until tomorrow morning...the vet and I chatted about the possibilities earlier today. They found an enlarged lump just below her breastbone that the vet suspects is her liver, enlarged from infection, or even possibly a tumor...she hasn't been eating much and was dehydrated too. The vet also did a stool smear and found what she thinks was an abnormally higher count of bacteria so she could have an infection which at this point would be the good news, because antibiotics are the cheapest direction to go. If it something like EYP, cancer or some other reproductive or internal problem, it's hard to say what without X-ray images which are too expensive or bloodwork...and even with all that there would be little they could do to treat such things. The vet suggests we try a course of oral antibiotics and see what happens over the course of 5-7 days. If she doesn't get better, or takes a turn for the worst, she said to bring her back in and they will euthanize her.Poor baby girl. Prayers that she gets better.
That's the crummy part about taking chickens to the vet, it's so expensive just to try to diagnose them with all the testing that is needed. I think you are on the right track. Either this is something that will respond to moderate treatment such as antibiotic's or it's something serious that is not fixable anyway. I'd be doing the same thing.