It is unlikely she would need your help if she is broody and on the nest. I suspect our "Help" is a very poor substitute to a hen. Probably far more going on than we even know now. I imagine they can feel the chicks moving as well. I wonder of there clucking does anything to stimulate the Chicks as well. Just so many small factors that could be a part of the whole process. A hen sure has a lot more dedication than I have heard out of even the most obsessed incubator operator.