Hens either go broody or they don't and it's up to you to leave them to it or try to break them. A hen that is going broody will usually lay quite a few eggs first and then start spending more time sitting around in the nest, even if you remove the eggs. She will find her favourite nest spot and sit on it for hours at a time for a couple of days until her egg production stops and she starts displaying signs of the hormonal changes. At this point if you or another hen moves toward her she will puff up her feathers and possibly peck at your hand and give a warning growl. The way she sits on the nest will be more flattened than when egg laying.
The best way imo is to collect her eggs every day as normal and not refigerate them. Keep them fat side up in a cool place away from draughts or intense heat or cold and mark them with pencil to show the dates. Wait til you have as many as you would like to hatch, say 12, then every day when she lays another one, put it in with the 12 and bump out the first one to eat or whatever. Eat the oldest one, save the newest.
Then once she has been sitting and puffing up for a couple of days, put the eggs under her at night and keep an eye on her.
A broody will usually get off the nest only once a day for up to half an hour.
