I've had chickens for 10 years but have learned more here on backyard chickens in the last month then I thought I ever knew. I made a candeller and candled her eggs on day 2, day 7, day 10, day 14, day 19 and yesterday when they were due to hatch. I've never monitored it so closely before. I had hens hatch out eggs before but it was a surprise and only one of my hens let me do anything. It is very cold here too and I don't think the heat lamp does that much, I could be wrong though. I agree that hens have been doing this for many years and if she wants to she will hatch them out and keep them warm, as long as you have a place to keep her away from the other hens. I lost 6 eggs from other hens breaking them on her so I put a grate over her nesting box and she feels very secure there. I kicked this particular hen off her nest for 2 days before I let her set because I was afraid of the cold. I will probably move her and her chicks to a brooder in a couple days to make sure they stay warm.