How do we prepare or girls for the winter?

Mine don't perch.  I found last winter they all snuggled up together either in the house or in the nest box.  It was really cold last winter - it was -11c for several days and thankfully they were all fine.  We had a lot of snow as well.  The one thing to watch out for is the drafts which I believe can do them harm.  I think they are good at keeping themselves warm.  I will put an extra thick layer of shavings in aswell which should help.  I have one who has half moulted and I think one or two more that are about to start so hopefully they will be getting their feathers back before the really cold weather sets in.  For the daytime I have made a shelter so they can get out of the wind and rain and hopefully will put a dust bath in there for them but they usually choose their own dust bath so the one I put in might not be up to their high standards

have you tried blocking off the nest boxes at night. this might encourage them to use the perch

Mine all decided to moult last year during a really cold snap, snow and all. Garden looked like a feather pillow had been emptied over the snow! Chickens were threadbare but managed to do fine, cuddling up etc at night and running around a lot keeping warm during the day.

Feeding cracked corn in the mornings during winter helps to raise their body temps, but don't use this as a staple feed. Mine also like warm porridge made with water! Also layers mash or pellets mixed with warm water.