I see many who say they should not sleep in the nesting boxes. My best friend, who raises chickens, said she’s never been able to prevent it in the winter. Why do we not want them sleeping in the boxes?
They poop a lot when they sleep. You don't want poopy eggs.
I don't know how your friend's coop is set up or the flock make-up. Mine do not sleep in the nests in winter and with my juvenile roost set up it's really rare in the summer when I have a lot of immature chickens afraid to sleep on the roosts with the adults.
Chickens sleeping in nests is pretty common, but when they do there is a reason for it. If you can figure out the reason you can fix it.