The only sure-fire way I've been able to break mine is caging them (other than letting them hatch and raise chicks). I put a dog crate in the coop, with food and water, and then keep the hen in there for three days. It's always worked for me!
I just read of a method someone used that worked several times for them. It does require a wire bottom cage, also a small fan. Put her in the cage, no nesting material, prop the cage up, put a pan of water under the cage, run a small fan over the water. It's the cage method with added cooling to her bottom side.
I've had them stay broody for months sitting on golf balls of just an empty nest.
The "broody coop" should work. Always has for me but after you've let them set for a few days it may take longer to work. All I've ever used for a "broody coop" is a wire cage off the ground (or floor) with food (layer ration) and water. Regards, Woody
Give her golfballs or plastic easter eggs. After a few days she'll realize that they aren't real eggs-- or at least mine did.
I think you just got lucky there. Giving them anything that resembles an egg is usually guaranteed to make them brood even more stubbornly. It was hilarious to watch ours fiercely brooding a golf ball until we accumulated a clutch of real eggs for her!