How do you know if they are sick or broody?
Your hen sounds like she's broody. Growling, refusal to leave the nest, and irritability are signs of broodiness. Broody hens will determinedly sit in a nest even if you remove all her eggs. There are several ways to "break her up" (make her stop being broody) including repeatedly moving her out of the nest. She may not lay for awhile even after she has quit brooding.
But in my opinion, if you can have her hatch some eggs, let her! Watching a hen care for her chicks is really a great thing. :)