If it is unusually cold she might be trying to keep them warm..or..she is in moult and wants to avoid the cockerel..roosters and cockerels usually leave a mother with chicks alone and do not try to breed them.Quick broody update.
Even though they're on the roost at night, mamma did NOT kick them to the curb like she did last time. She's still hanging out with them and caring for them.
ETA: Just went out to be sure everyone got in and she's on the floor w/the kids in their place again after having spent 2 nights on the roost. So this is a new way of mothering for her.