Today I noticed a hen that could not use one leg. She also has a purple-black tinge around the edge of her comb, as well as a prominent keel and fluid in her abdomen, plus missing feathers around her butt despite being at the top of the pecking order and lately she has had weak eggs, but all the other birds did too so I assumed it was not enough calcium in their feed, though now I am thinking there might be something else. She seems completely unbothered by all of this, and was calmer than usual when handled, though she was hungry and dehydrated from not being able to reach feed or water for several hours at least. She has not come into contact with any new chickens, and has no apparent injuries. If anyone has any idea what this might be please let me know.