Hi
Just found this post.
Unfortunately it does sound like Marek's. How old is she?
My experience is that as long as they are interested in food and prepared to fight it, I offer good nutrition (Nutri-Drops are good) and supportive care. Once they stop eating, I euthanize. I have had some make full recoveries and some make sufficient recovery to go back to free ranging with the flock but it took months of supportive care and sunshine, grass and the company of another chicken were the key factors in the recovery. Sunshine and grass being 2 options that are difficult to achieve in the UK at the moment. Unfortunately I have also had others that did not make it and had to be put out of their misery.
I did my own post mortem and based my diagnosis on the tumours I found and that I had several juvenile birds become lame within a week, so I'm afraid I can't really offer advice about professional necropsy here in the UK.... possibly veterinary colleges would be the best bet but Defra could maybe advise on that.
Your chicken hammock looks great but perhaps would be more successful if the box was deeper so that she is fully suspended and may then be less able to turn around etc....A cardboard box is an easy option especially with a bantam as they are so light weight. I use an old t shirt and just staple it to the top edges of the box. It's something you need to fiddle about with until you find what works for you and your hen. It's good that she is keen to eat though. Feed her different treats on different days so that she doesn't get bored and keep her food moist....scrambled egg with soggy bread or fermented pellets, cat food, bit of tuna or sardines, bit of meat(avoid too much salty processed meats but a little bit of ham once in a while is OK If you can put her somewhere like a sunny windowsill where she has some outlook, if you have her in the house or within sight of other chickens if you have her caged outside, that will also help keep her spirits up, but be aware that she needs to be well sheltered from the weather and draughts as she will struggle to maintain body heat whilst fighting the disease.
Good luck with her and keep us posted on her progress.
Regards
Barbara