Corn does not have but half of the protein and none of the other nurtrients needed for a chicken laying eggs. They will eat it in preference to the chicken feed which is not good. Yes it is cheaper, but for $4 more a bag, they will get better nutrition. All flock feed or layer feed has all of the vitamins and minerals, and everything they need. I agree that she might have a liver issue because of her yellow skin. How does her lower belly between her legs look? Is it enlarged, spongy or tight, compared to othes? She might develop ascites or water belly. Corn or scratch has a tendency to cause them to become fat and that increases chances for fatty liver disease and early death.
It is hard to know what happened to her feet. She has scally leg mites, and most of the scales are missing. She may have been pecking at her own feet, but sometimes rats will bite feet and toes off while they are roosting. She definitely needs to be in a warm place getting a daily warm soak to her feet. I would use either Epsom salts, a little dish soap in the water, or some Hibiclens. Apply plain Neosporin or Triple Antibiotic Ointment daily.