The two things I think of reading your posts is egg bound/egg yolk peritonitis or coccidiosis. With a lubricated, gloved finger you can do an exam of her vent, gently probing for an egg. The first bath may not be enough if she has an egg stuck. Then consider cocci because if she is ex-battery, she may not have any immunity built up to it. Can you get Corid or amprollium in the UK?
Its not coccidiosis I an leaning towards egg bound, how many baths and how often would you recommend? She still won't eat or drink, I have to give her water in a syringe, she has gone to bed now, although she is stood up sleeping
Ok so after some advice I now feel stupid, she isn't egg bound and it isn't respiratory, it's lice feel proper stupid now, so I have dusted all my chickens while they were roosting, and the coop, tomorrow I will do all the next boxes, so relieved it wasn't egg bound
I'm so very sorry. I'd been watching this thread to see if someone could determine what was wrong. Wish I could have been of help but I'm relatively new to chickens and didn't have a clue.
Unfortunately I think she was very egg bound, I tried everything I could, but I think a mix of everything was just to much, she was heavily egg bound and also a huge lice infestation, so this morning I have done a very deep clean, and treated the coop, and all my remaining birds, so fingers crossed no one else becomes ill due to lice :-(
Sorry for your loss. Do you have Sevin dust in the UK? It is very good for lice and mites. You can put the chicken and dust into a garbage bag, and pull it around the neck of the chicken whilt shaking the dust all over them without it getting into the eyes and nose.
I have dusted all chickens and coops today, I havent seen sevin, but I got a poultry lice and mite powder from the farm supply shop, so today I striped the coops, cleaned them and disiinfected everything and then dusted all birds and coops, I will repeat in 7 days then every 6 week's