@Shadrach and all ex-batts followers, I'm dealing with another very unwell hen and hesitating whether to take her for a 1h45 ride to the vet. Would you have an opinion ?
https://www.backyardchickens.com/threads/is-it-wise-to-attempt-a-1h45-trip-to-the-vet.1539953/
I wouldn't have considered it if I hadn't lost Vanille on Thursday ...but I'm not being very rational at this time.
I do have an opinion.
It rather depends on the vet. A livestock vet will tell you to kill her. A pet vet is very unlikely to know or care much about a chicken and may take your money but not tell you the truth..
If one can't see what is wrong (things like water belly and prolapse right down to mites you can see) then it's an internal problems which needs tests and equipment and experience in dealing with chickens. I was extremely lucky in Catalonia to find Gloria (vet) who specialised in birds when she was training. There was one other person she told me, an old man who used to bring his rooster, that had brought chickens to her since she had joined the surgery.
The best thing about Gloria is she told you the truth. She was able to say "I don't know and don't have the equipment to find out whats wrong. I could guess but I could be wrong."
So, there's the first consideration; do you trust the vet?
The probability is that whatever illness she has it's going to be terminal. From the little experience I have of Ex Battery hens they are fine and then within a few days they die. One gets to know when it's just an off day or two and whether they are going to pull through. I think I'm on death 10 or 11 now and most have died quickly.
So then there's can you and should you help them.
Given the life and the damage typical to the battery breeds part of me feels as I think Ribh does that a quiet death somewhere in familiar surroundings, with whatever friends and enemies they may have made while living together, is the more dignified death than what often means isolation and stress involved in trying while the keeper tries to get the chicken well.
We humans haven't embraced our relationship with death well. It effects our view in as much as we are often convinced everything is fixable.
I set out what I was prepared to do and what I wasn't at the beginning. I think it's something important for Ex Battery hen keepers to do once properly informed on life span and likely terminal illnesses. Even if I could find a vet who knew something about chickens, every one of these Ex Battery hens is likely to be dead by this time next year. That's an awful lot of vet visits.
I wouldn't take her to the vet. If you can bear it watch her die and if necessary intervene and help her on her way. Strange though it may seem it's good for you and I believe good for the chicken.