It could just be that she (and maybe a pal) preferred to lay outside the box. When you thought she was not laying, she actually was...just where you just found the eggs, rather than in her nesting box. You'll know if she's broody--she will sit on her eggs all day in a trance-like state, getting up only briefly to eat and drink. And then she will cluck and puff herself up, warning everyone away from her. None of my flock messes with the broodies, not even the roo!