If she's staying in the nest box and got an egg or something resembling an egg under her she'll refuse to get up, probably screech at you and peck you if you try and take it from her. I don't know about Silkie behaviour in general, but my broodies get very aggressive. They'll puff up, growl at me, peck me and when they do get up they'll walk around making clucking sounds, drink some water, eat something, have a dust bath, chase whichever chicken's nearby around a bit and go back to the nest after a few minutes. There they spread themselves out over the eggs and glare at anyone who comes near.