To me this sounds like an old constantly broody hen that is getting bullied by her flockmates. And because of her constant broodiness she will become malnourished and weak.
Here is what I would do:
Separate her in her own space or wire dog crate.
Serve a nice bowel of scrambled eggs with...
A greyish face is not normal, so you better get a closer look in case she is suffering from an injury or poultry mites (bloodsucking kind) or lice.
Some more information would be helpful:
How old is she?
When did you last deworm your chickens?
What exactly do you feed them?
Do you have a...