While I disagree that someone can know everything about chickens, I don't think cracked corn can cause too much of a deficiency if it is being fed along with layer feed. Your bird is probably molting, but if she shows new symptoms you can update us on her condition.
Thank you! There are bantam and standard Cochins. The bantams are about the size of a basketball; the standards are about twice that size. I purchased both of my girls at a local ABA show from good breeders. Shows are really great places to talk to experienced breeders and buy nice birds.
Does she have a fowl odor or discharge coming from her vent? It's possible that it could be vent gleet. I would research it and see if the symptoms match because it is important that it's caught early.