A year ago I had a hen doing that. It turned out she was egg bound and trying to lay an egg that wouldn't lay. I lost her, and when I did a necropsy, she was full of yellow puss, so I'm guessing it wasn't the first time it had happened. She was our favorite hen, and it was a real blow.Ok that's too bad.
About the hen...
Sorry I said that in a confusing way. I didn't give her any eggs. I meant that if hens are broody, don't they sit in the nesting box all of the time besides a small break? She doesn't puff up and growl or anything of that sort when I enter the coop
You might feel around (gently) below her vent and see if you can feel anything in there. There are lots of threads on what to do for egg bound hens. I've not ever gotten any of them to work, but others have.