One of our RIR's has died.....I have no clue what it could be.

My son just came in and said one of our RIR's was dead. Sure enough it was laying there in the coop gone. We let our bird free range during the day (just around the house, while we are here) and she was not dead this morning when he let them out. He found her in there when he was locking the chicks back in the coop. She looked fine except her comb and face were pale, which I am assuming that is because she is dead. My husband will dispose of her this evening, but is there anything we should look for before he does that? Her feathers were not ruffled or anything and it doesn't look like a rooster was too rough on her, no blood nothing.

My kids are worried that it is too cold for the chickens now that winter is here in central Ohio. But RIR's are pretty hardy and the temps are only getting into the 20's at this point. And, like I said, it was not dead this morning, which is when I'd think you'd find them dead from cold. We have a nice sized coop with fresh bedding and good ventilation.

Just FYI, we have 30ish various chickens. Two EE Roosters, 4 EE hens, 4 BO hens, 4 NHR hens, 4 RIR hens, 4 BA hens and a few bantams....

Does anyone have any ideas? We really care about our chickens and I am concerned that we should be doing something....

Julie