You could try putting a couple of warm dummy eggs in the nestbowl and lock the hen in the nestbox but I'll doubt if she'll sit them. If she doesn't sit them tonight remove the dummy eggs and let them go down again under their own steam.
My hunch is that the egg hatched today whilst the cock was sitting, when it was the hens turn to sit the nest she was wary/uncertain of the newly hatched chick so much so she didn’t cover the nest.
Try resizing the photo in you photo editing software then save the photo as save as. Reduce the size by 50% to start with and if that dont work reduce it by a further 10% and so on.
The photo was taken by my son-in-law, he's a twitcher and a Ranger over at the marshes, you can imagine the heated discussions that go on in this house when he's over.