You mean this one? She does look like one, it's hard to tell when they are all fluffed up. http://www.feathersite.com/Poultry/CGA/Cornish/BRKCornish.html
At first I was thinking she was maybe a very poorly feathered wyandotte, but the comb is different maybe a mix? The reason she is all puffed up and won't get of her nest is because she is broody. You can break her from being broody by...
Amber White pullet.
Dominique rooster ( does he have a single or rose comb?)
Red Sex Link pullet
Silver laced wyandotte cochin, Amber white pullets, and a Light Brahma in the back.