My 4 hens are 16 weeks old. They've been together since they were chicks. Up until recently, they all roosted comfortably at night. For the past 2 weeks, I have been finding one of my white rocks on the coop floor while the others roost above her. She is NOT at the bottom of the pecking order. I'm worried about when it starts to get cold and she's alone with no body heat at night. Should I be concerned?