Actually I fed mine starter/grower because it's a bit higher in protein and she's not making eggs so she shouldn't need the calcium, I figured. Besides, I knew she would need this when the chicks hatched, as it is what the chicks need. She would eat the layer in the feeder for the others as well as this.
I kept feed and water in her broody pen but she took very little of them. In the AM when I opened the coop she would stand up off the eggs, so I opened her pen, and she would go out and do her thing for about 20 minutes, then return to her nest. I'd close her back up then to keep her from being bothered by the others (her cage was in the coop.) I found one broody poop in the pen; guess she got hungry or thirsty that day, and maybe she ate and drank more than I thought during the day. So if I do it again, I will continue to keep food and water in there.
I tried to get her back off the eggs 2 or 3 times during the day to eat and drink again, but she wouldn't. However, in the afternoon she would eat a bit off my hand, so I gave her some grower and something like watermelon or tomato for the water in it. Even then I had to prod her a bit to get her eating.
I'd keep scratch to a minimum during brooding as it is lower in nutritional value, and they usually don't eat much, so they lose weight, while being broody.