It may be that she has an impacted crop. I would try gently but firmly massaging her crop. If she is impacted she will probably enjoy it or at least tolerate it. The crop is a pouch where food that has been eaten through the day is stored to be slowly released into the digestive system at night whilst the chicken is sleeping. The outlet can get clogged or silted up with fibrous material or a large object (some chickens will catch and eat a whole mouse) That can plug the system up preventing any food and sometimes water getting through effectively starving and or dehydrating the chicken which then becomes week but is sometimes also ravenously hungry, eating more which makes the crop more impacted. Eventually, if the blockage is not cleared they will die. Isolating and preventing access to straw, hay, grass and shavings and giving only very sloppy watery feed perhaps with a bit of olive oil to help lubricate things and then gentle massage from the bottom of the crop upwards several times a day for 5-10 mins.... chickens make surprisingly good stress balls. If you are not making any progress after a few days it's time to try something else.
I must confess I had the thought about Marek's too just because she appears twisted. The vaccine doesn't always prevent Marek's but lets not get into that right now and just hope it is an impaction that you can clear.
If you fail to shift it with massage after several days, some people have had success with using Dulcolax and the final options would be vomiting by holding the bird almost upside down and massaging the crop to try to get the bird to regurgitate the blockage or crop surgery, which I have done twice and is not as complicated as you might expect. It involves cutting a small incision through the skin and into the crop, teasing out the fibrous material, flushing with saline solution once you have it empty and then sticking it back together with super glue. I appreciate it is not something everyone can manage to do though, but a veterinary should be able to do it if you cannot. There are You Tube video tutorials on it if you are interested.
Good luck fixing her.
Regards
Barbara
