If you shut her into a pen by herself, yes give her a food and water dish inside that pen.
If she stays in the pen with the rest of the flock, she can help herself from the usual feeder and waterer.
Broody hens prefer to eat and drink when no-one is watching, but you can gently feel her crop. If it has food in it, she did eat that day. (And if she ate, she also got off the nest to stretch her legs, and she probably drank and pooped as well.) I have found morning to be a good time to check the crop-- it seems that quite a few broodies will eat first thing in the morning (although of course individual hens may do different things.)
Broody hens do not eat as much as other hens, because they are not laying eggs or running around using a lot of energy. So as long as she is eating, I would not worry about how much she is eating.