Just give her a little food. No need for a heat lamp, maybe a heating pad. The chicks will survive, the hen will keep them warm and find them food. One of my hens once went broody during the winter, sadly she was eaten by a fox... Her 10 week old chicks survived 10 degree weather. With no mum and no heat lamp and no heating pad... But they were also eaten by the stinkin' fox.
My little Black Japanese Banty went broody on me two weeks ago (she's actually on day 17 today) but she's nesting in the coop. I'm in Northern New York and I understand the nervousness with it getting colder. (She's my first broody.) You can't help but worry. Two days ago my Spitzhauben decided to go broody as well, so if she stays with it hers won't hatch until around the 22nd. I have no electricity in the coops so it's a litte nerve racking.
