All the answers below work to some extent, the main theme in each answer is the same. The broody hen just wants to be left alone and if she is bothered too much she will stop brooding. Keep her occupied and away from the nest she has chosen. Remove any and all eggs, move her as often as possible and bother her, making her uncomfortable. This will work in most cases.
Why not just remove the eggs? She willll sit on nothing for a couple days but she will figure it out! Dunk the hen's belly in a pail of cold water until feathers are soaked several times a day. Continue soaking until the hen ceases being broody (usually couple days). Tried, tested and true. Removing the eggs is best way, but be careful; depending on the breed, some hens will be very stubborn. I once had a hen who went broody, we candled the eggs after a week and saw they were bad so we removed them. She would not leave the nest. We kept feeding her at the nest but we had to get her off. We forced her off the nest into a nearby pen with the other chooks. She paced the fence for days, dug under the fence and raced back to her empty nest. She had lost a lot of weight and by the time she gave up on her empty nest more than three months had passed. === === I usually put the hen in a pen with no roost and then put a rooster in with her. Young roosters that are very "sexually excited" work best. She will get bothered and will get out of the broodiness stage. Also you could try putting her in a wire pen with a wire bottom off the ground. The wind will blow under her keeping her cooler and she will get out of the broodiness mood.