My Chicken won't leave the nest box!

Only thing is she is Broody. If there are any eggs in the nest box then she is sitting on them "broody" and waiting on them to hatch. This will go away when the eggs hatch or in about a month if they haven't take them out yourself and she will soon go back to normal.

If she is the only bird in the coop and there is no rooster then there is no way the eggs will ever hatch, they haven't been fertilized. If this is the case in about a week go ahead and remove the eggs before they rot and start smelling and she will get back to normal soon.

If there aren't any eggs she will figure it out on her own in a week or so and resume normal activities.

 

What breed is she? If you reach in at her does she puff up and 'growl' at you? Some will actually go for you and try to take a chunk of your hand, so be careful when trying this test! To me she sounds broody, but if she gets mad when you try to reach into her nest, you know for sure she is. Also look at her keel (breastbone area) and see if she's pulled out feathers to make a bare patch. That's a definite broody sign too.

Also, !

 

Sounds broody to me. They do puff up and sometimes peck at you when you try to move them. Wait it out or cage her as mentioned in other posts. Caging her with ventilation underneath eliminates the warmth that she's trying to produce and nature kind of talks her out of the idea of hatching eggs.