Do you isolate a broody hen?

Move her so she has her own private place.

Otherwise, other hens will drive her from the nest or when she gets off the nest to eat, drink and poo other hens will likely get in her box and lay and when she comes back she will pick another nest box with eggs and of course the eggs you want to hatch will go bad.
I simply put my broody's in a wire dog cage, works like a charm.
I put foot and water in and clean up her poo once a day.

 

Definitely seperate her. I have a broody hen who went broody on April 5 and other hens got into her nest and cracked eggs, she kept adding eggs (she was trying to set on 18!) and it was a mess!

I finally got her moved into an old cage I had, but if you do move her into a cage, do it at night. I tried to move her in during the day and she flipped out, but at night she was fine with it.

 

Definitely do all your dealings with her at night. Some hens are less determined than others, and might get spooked off their nest, never to return. I try to make the transition as seamless as possible. Sometimes you can just put a barricade around the hen right where she's made her nest, or move her inside the nest box to the secluded location. Or slide a cardboard box up under her & her nest and move it all together. But if that's going to be too much fuss, you can try moving her separately from the eggs. Often the sight of those egglings in the new nest box is enough to inspire the hen to get right back on them.

I wish you & your hen the greatest of success! It's so fun to watch a Mama hen tending to her chicks.