Layer feed can hurt non-laying birds because of the high amount of calcium. You definitely shouldn't feed it to chicks, once they hatch.
I maintain separate flocks; the layer flock eats in a completely separate area from the non-layer flock and receives different feed. I do this because Layer feed is really cheap.
You might start slowly transitioning the whole flock over to meat bird or allflock or chick starter/grower. Pick feeds between 18-20% protein. Provide calcium on the side so that the laying hens can fulfill their needs. That'll allow you to integrate chicks and adults a few days after hatch, so that the mum's still protecting the chicks violently, and she'll take care of integration for you.
I free-range, so my layer and juveniles sort of drift together and naturally transition into the adult flock. It avoids a lot of drama, but can lead to increased predator danger.
Don't put food and water too close to the broody hen. It can attract rats, ants, mice, or predators and can endanger the nest. She'll get enough to eat when she gets off the nest. It'll encourage her to stretch her legs and dustbathe as well, which is a very important activity for a setting hen—they tend to get mites and lice.