Do you have fake eggs in the nest boxes! They may need to be reminded where to lay. You need to take the spot away that they are laying in now. Use wood at an angle or something that they cannot get inside or on top of. It is no fun...
Last year we used extra light in the winter and the laying never slowed! This year we have not used extra light and we are down to about 2-3 eggs a day out of 10 so I would say it works good!
Is she the bottom of the pecking order? Have you ever witnessed an attack on her? Is it only one attacking her or a whole group? Lots of times there is nothing that can be done about it, chickens do what chickens do full time. It is...