I encourage the hens here to sit in their flock coops. It saves so many integration problems and often means the chicks get added security from the flock because mum will try to move about with her group. It has also meant here that the chicks hear other chicken voices while they are in their shells. The coops here re off the ground but the nest boxes are on the floor of the coop. this allows the mother to get her chicks out and about at will when they've hatched. I've had mothers kill their own chicks, but I have never had chicks attacked by other hens, or roosters; told off once they are old enough sure but nothing more.