is she calm and sitting comfy when she does it? listen close, is she making a sort of crunchy, grinding sound? if you can hear a grindy, snapping sounds... don't panic! mine do it when they are settled. usually toward evening. i am not sure exactly what they are doing, but i call it "beak grinding" i think it might be a keets way of helping avoid overgrown beaks. i like to listen to it cause i know then that they are truely content.
if no sounds, is kirby preening at the upper breast feathers often? if so, come back and explain, ok?