You can also slip a few day old chicks under her at night -- probably best to let her set a week or two first. I did this last month, just removed the golf balls I was letting her try to hatch, and replaced with feed store chicks, well after dark. Worked like a charm.
All about broodies, in case you want to read more:
http://www.themodernhomestead.us/article/Broody-Hens-1.html
All about broodies, in case you want to read more:
http://www.themodernhomestead.us/article/Broody-Hens-1.html