A hen stores up a lot of fat when she is laying eggs. It's perfectly normal and basically what she lives on while she is broody. A broody hen will lose a lot of weight while sitting on the nest, but in a normal cycle that's just excess fat stored for that purpose. If she is allowed to stay broody without giving her eggs to hatch or chicks to raise, that can eventually get unhealthy. I think the least cruel thing to do by far is to break a broody if you are not going to let her hatch or raise chicks. I use the wire bottom cage method. It can take a few days or many days but as long as she has food and water the hen is doing fine. It has always worked for me, but some hens take longer than others.
The longer she is broody, the more of that fat pad the hen uses up. Before she starts laying again, she has to replace the fat she used. That's another reason to break her fairly early in her cycle.
There are a lot of signs that a hen might be broody. Staying on the nest a lot, being protective of the nest, fluffing up, growling, pecking, walking around fluffed up and making a steady pukking sound, such as this. But I have hens that do that and never kick over to full broody mode. I currently have one hen setting on a dozen eggs, just took one out of my broody buster, just put another in my broody buster, and have had one walking around for about a week fluffed up and making that pukking sound but still laying eggs and not all the way broody. She may kick over any day to full broody mode or she may break herself and return to normal. My test to see if a hen is truly broody is that she has to spend two consecutive nights on the nest instead of roosting in her normal spot. I've had some spend one night and never go back, but if they spend two consecutive nights they have always stuck it out and hatched eggs for me.
Good luck!
