The best way to break a broody is to keep her in a small cage off the ground with a wire bottom for three or four days. The wire bottom keeps her undersides cool, which seems to help. Give her food and water and she should be fine. Do not give her anything that looks like a nest or nesting materials.
If you don't have the wire cage, any small cage will do, but it might take a little longer. Just find a way to keep her from going back to her nest.
I saw a post where someone put coldpacks in the nest. The cold supposedly cured the broody. Never tried it myself.