Before a hen even starts laying eggs she builds up a reserve of fat. I've butchered lots of pullets, hens, cockerels, and roosters, the difference in fat between the girls and boys is tremendous. The reason the girls get the fat is that is what they mostly live on if they go broody. That way they can stay on the nest most if the time instead of being off looking for food. They will loose weight while broody but that is not a problem, it's just fat put there for that very purpose. The way we keep them they can go to the feeder and fill up when they come off the nest. In the wild the food is not available like that, they have to search for it. That fat does provide enough for them to live off of.
I've seen a broody hen come off her nest twice a day and stay off for over an hour each time. I've seen a broody come off once a day and only stay off for 15 minutes. Both had great hatches. Often I never see the broody come off the nest but since she is not pooping in the nest I know she is coming off. Broodies should know instinctively to come off of the nest to poop so they don't poop in the nest and mess up the eggs. While they are off they will probably eat and drink, they may take a dust bath, but their real purpose is to take care of the eggs. You can get a hen that is messed up as far as some of those instincts go, with living animals anything can happen. But I generally trust my broody hens to know more about being broody than I ever will.
I let my broody hens hatch with the flock. Part of my daily routine is to check under them for any eggs that don't belong after the others have laid. it doesn't hurt them to toss them off of the nest at this time. If they are committed broody hens it will not break them from being broody. When I do that they squat on the coop floor for several seconds and then either run off to get food, water, and maybe poop or they move back on their nest.
After several weeks a broody hen will use up all her stored excess fat. Most will break from being broody then if not before, but a few don't. If you are not going to let her hatch eggs or raise chicks I think it is best to break her as soon as possible. It's just kinder to her. I break mine by putting them in a wire bottomed elevated cage so air can get under her. I provide food and water but nothing that looks like a nest. After 72 hours I let her out. If she goes back to her nest she goes back in that cage but usually three days is enough.
Breaking her will not prevent her going broody again later. It hasn't mine. Some go broody often, some only occasionally, and many will never go broody.
I think I've answered all your questions. If not, let me know. My main suggestions are to trust your broody and if you are not going to let her hatch or raise chicks break her from being broody now. It's the kindest thing to do.
