Why didn't you separate your broodies from the rest of your flock, especially since you know the hen has been killing chicks? My hens brood in a bird cage, but I've used 5 gallon buckets, dog crates, cat carriers and all other sorts of things. Find a large cardboard box, flip it on its side and put some chicken wire over the opening. Its your job to keep them safe, the chicken is just doing what some chickens do. Good luck, I hope you get it all sorted out.
Nikki
Nikki