Hi! Welcome to BYC! Am I assuming correctly you have no other chickens? That the broody hen and her chicks are your first?
If so, there's no reason why you can't install her comfortably in your coop. She'll probably prefer a nest with straw or clean wood shavings that's near ground level. Provide water for her and the chicks but take care that you place rocks or marbles in the tray so the chicks can't fall in and drown. They can be very clumsy during their first week.
If you provide chick starter crumbles, that will be adequate for the first three months of their life or even longer and it doesn't hurt the hen to eat it. If you want, you can start feeding them all layer feed once the pullets begin to lay. Offer oyster shell on the side and you have it covered. Most chicks show no interest in the oyster shell, from my experience.