I have my chickens for bug control and fertilizer. I let the hens sit if they want to and don't normally interfere. I really don't care if they ruin eggs as I normally end up giving most of my eggs away anyway. I've had many go broody and a few have been great. Others just don't get it. They...
If she sits in the nest box, she isn't going to take them around to eat and drink. A good broody will leave the nest and any unhatched eggs to take care of live chicks.
Is she a first timer? Sometimes the new ones take a bit to get used to it. I would separate her with the chicks for a bit...