I've always had success breaking a broody as follows: Isolate the broody in a cage, sectioned-off area of the coop or run, or other area away from her nest. Make sure it's secure enough that predators cannot get to her, as she'll be in there for 2 or 3 days and nights. Make sure she cannot...
Not all broodies will foster chicks. If she's a proven broody - that is, has successfully raised chicks - she's more likely to accept them. When fostering chicks to a broody, the hen should be broody for at least two weeks, and the chicks should be no more than a day old. If the chicks are...