I know this post was months ago, but I have seen alot of this happening with ayam cemanis, I believe from too much inbreeding.. Or, perhaps she had coccidiosis and it stunted her growth. Did she ever grow out of it?
Set traps with a can of tuna or sardines inside every night by the coop. Once they discover they can get food there, they will just keep coming back. I shoot them. But I'm sure if you don't want to, maybe someone could relocate them. We have coonhounds and actually built the new chicken coop...
Could very possibly be a mink, I'm not sure if you have them where you live but I had a completely enclosed chain link pen with no gaps at all and they actually went through the little squares. They only ate the head for some reason.