Never leave a broody hen broody,unless she is hatching eggs. This is very dangerous to her health. She is probably malnourished,hens don't look after themselves when they are broody. To break a broody,place her in a cage with a wire bottom,you want air to circulate under her and on her breast. Broodiness is tied to elevated body temp,you want to cool her down. Place her where she can see light(broody hens love the dark to hatch eggs)you want to do the opposite of what she wants. Make sure she has food and water,i would also give her some vitamins because of her health. Leave her for a couple of days,let her out,if she runs right back to her nest,she is still broody. Put her back into the broody box,try again in couple of days. When she is done being broody,she will resume normal chicken activity(scratching,dust bathing,etc.). This is probably going to take awhile to break her,the longer a broody is broody,the longer it takes to break.
