Do you want to keep the brooding hen setting? Then move her to her own place well after dark. She needs to be by herself with her own food & water. It can be a kennel, cage, a different pen, or a barricaded section of the main coop. Make her new place shady with extra feed bags or whatever for a few days to encourage her to stay there. After a few days it should be apparant whether or not she'll stick with the job. If you want you can then swap out the eggs she began with for others you'd rather she hatch.
Make any changes with a broody hen after dark, they're less aware at that time.