I have never seen another hen help with warming chicks like that, but I have had hens hatch here in Southern California in the winter, and they all did fine. The chicks will kind of dive into the mother's feathers and find themselves a warm spot. At night, mine are usually in the same nest box or kennel in which they brooded, so it's tight and cozy. Occasionally, a hen smothers a chick, but I do not think it is a seasonal problem because I have seen that happen in all kinds of weather. I know the feathering on a silkie is different; my experience is with more standard breeds. Does your broody have a separate and enclosed nesting place?
I have month old chicks from the incubator outside right now. They have been out full time for the last two weeks. Prior to that, I was bringing them in a night as it gets cold up in the high desert this time of year. I put a seed heating mat inside their kennel for the first few nights outside, then moved it to under the kennel and shut it off once they were nestled together for the night. They never seemed to need it during they day. I just took it away today on their one month birthday. Between a concerned flock guardian like yourself and the mother hen, I'll bet all will be well with your little chicks. If you're like me, you'll also become addicted to setting every broody hen that turns up...
