Why not just block the nest box the broody is in off and open it up a once or twice a day for her to get food and water
I put a board up in front of it so there wasn't room for another hen but uh. . . they got in and laid mostly on her, till they slid down into the board i propped up, and knocked my board down. They are determined for sure. It's pretty much too late to do anything tho because she should have a few already hatched under her. I will be checking her daily to find out when she brings the newbies out of the nest and confiscate the rest of the eggs then. Then i think i'll adjust the size of my nesting boxes. I have English Orpingtons so i made them a bit roomy.

