I have three hens and suddenly, for the last two nights, one of them won't go into the roost box at night. They free range during the day in our garden and then we put them into the coop late afternoon. The other two go up into the roost box at dusk but Henny just sits on the lawn in the base of the coop. I'm worried if I leave her there and leave the door to the roost open, a fox could dig underneath and get all of them, but don't feel I can shut her out either. The last two nights, I've picked her up and dumped her in the roost box. Any ideas?