Hens go broody when you don’t want them to… and won’t go broody when you do. 
Try putting a light in coop at dusk.
I use a battery operated puck light,
turn it on an hour before roost time,
turn it off after dark when I lock up.
I use a battery operated puck light,
turn it on an hour before roost time,
turn it off after dark when I lock up.
