If you're sure she's broody and you want to break her broody ways, you can either isolate her in a wire-bottomed pen/cage with no nest (but with appropriate food/water) for a few days, or dunk her bottom in some cold water. We have an old rabbit hutch that worked as our broody-breaker recently.
I'm assuming since she's broody she isn't laying, correct?
Alternately, you can give her some fertile eggs to lay on, but as winter is closing in - depending on your location and climate - that might not be the best idea.
Also, use the search function to read about how other BYC-ers deal with their broody hens.