Have you tried any of the traditional broody breaking methods on her? Only asking as it won't be very helpful to suggest things you have already done.
I, personally, use a "broody buster" - simply a basic wire cage that is placed in an elevated position (ie up on blocks) to allow airflow to get up under the bird through the wire bottom. In this cage goes the bird, feed and water -- no nesting materiel or bedding. Leave her in there for three days or so and then let her out - if she reverts to broody behavior simply put her back in the cage. Lather, rinse and repeat until she goes back to "normal chicken behavior" when released. My hens usually only need 1-2 3 day cycles to give it up.
All that being said - if you are not thrilled with having a broody bird in the flock you might be best suited to find a home that wants/needs a good broody as she may well just be a habitually broody bird and you may find yourself constantly having to "break" her. Me, I like a good broody and am always glad to have one in the flock as a good broody bird is worth her weight in gold.
