I had one hen raise one chick in temps like that, in the coop with the other hens. No heat. At the time, I did not know people separated broodies/mothers. The chick would go under her for warmth as needed. Feed starter or grower, not layer, which is fine for both.
When the momma got killed, another of the same breed took over the chick's mothering!
I have mostly heavy breeds and have never seen a silkie. Might be a problem if there are several chicks, as I understand silkies are small, idk.
A neighbor had a silkie disappear, then reappear a few weeks later from the woods, followed by several new chicks.