My pullets have not started laying yet, so not posting from experience but I have a question-- when I was growing up, my grandparents had TONS of chickens, as well as ducks and guinea fowl. Although they had at least 6 nesting boxes in the chicken coop I can remember the 2 at the far back were the ones used by ALL of the hens. So every morning when I would go out, I would gather eggs from those two boxes, but the other 4 were almost always empty. I always thought it was strange that the hens didn't mind laying their eggs mixed in with other hens eggs, but maybe it makes them feel it's a safe place.
Which brings me to my question---
Could you pick up Penguin's egg and put it in the nesting box and leave it for her and the others to see, at least for a day or two?
It might inspire the others, and steer her to repeat laying in the same location the egg is already at, rather than have 1 egg in the nesting box and another on the floor, since they try to lay all together to accumulate a clutch.
Would be interesting to hear if it would work.