Today I noticed that this chicken has a unusually large breast area. I was examining her and the "growth" is as hard as a rock and she has lost a few feathers on the underside of it. This feels like it is outside of the breast bone. I hope this is just something weird, of all the chickens we have had, we have three left. This one is the last that my middle child owns. Of her three, one ended up being a rooster that we had to rehome and the other died when our old plastic feeder exploded. This will break her heart if she loses all three. Any help would be great.