All pullets or female chickens go broody at one or more points in the year. Most broody hens will start acting a bit odd, seeming a bit lethargic or moody. Their personalities change pretty drastically. Nice birds can turn into vicious, grumpy, snarly, birds and grumpy birds get worse. On the good side it doesn't last long when you know what to do.
The bird is trying to brood chicks so think of a pregnant woman who's got a severe drive to nest and double it. She is wanting to raise baby chicks and is a ball of raging hormones. Here are some reasons why you need to stop a broody hen:
So that all being said, you need to start by removing any eggs including fake ones. Sometimes the hen will be sitting on nothing too. Try to keep them gathered promptly or she will go lay on them and guard them. Keep taking her off the nest and placing her outside with everyone else. The hen will growl, she may stick out her neck feathers like roosters do when they attack. Do not allow her to intimidate you or, like with any animal, she will use the fact that you back off to keep you from removing her. If you are nervous about her lunging her beak at you, use leather gloves. I can honestly say I have been fully attacked by a rooster and it just startles you. Their beak won't do too much damage, although the spurs on a rooster can really hurt you. They will usually just grumble at you.
What I do is calmly talk to her at first then put my hands quickly down at her wings. Wings slapping you tend to hurt or startle both of you. Pin her wings to her sides lift her up like a football and set her outside away from the nest. Be firm if she goes back, take her off again or just gently block her from going back until she joins the others. This can go on for days. Do not just scare your hen off the nest. This will cause too much stress and cause her not to lay in her nest anymore.
Once she stops staying on the nest and stops acting agitated she will start laying and all will go back to normal in a couple weeks. Keep in mind though, all hens do this so you may get one to stop and another may start going broody. I have three hens that went broody last year. This year I have already had one, but I have seven girls.
This year I have been trying to break a hen from being broody for the last two weeks. Some chicken breeds are more prone to being broody than others so learn what you can about your chicken breed. Some breeds are easier to break from being broody than other breeds. Once you get to know your flock you can see the signs easily and start breaking the broodiness right when she starts. Sometimes, she may run around and try to start fights with the other hens. Unless she's really hurting them it's best not to interfere. My hens will peck the grouchy one and not put up with her being feisty with them.
If this method doesn't work you may need to move your broody chicken into isolation for a few days. The best way to do this is to take a large tub and put a perch in it. Do not put any nesting material into the tub. You will need to put a wire cover over the tub to keep her inside. Provide her with food and water. Leave the lights on all the time and keep her in the tub for 48 hours. After that, return her to the coop and observe her to see if she has lost her desire to be broody. There could be a small adjustment period as she reintroduces herself to the flock, but nothing serious should come of it.
If you want your hen to hatch eggs let nature take its course if you have a rooster. She will lay one egg a day until she's ready, then sit in the nest to start incubating the eggs. They do not start incubating until they have decided they have enough eggs. This keeps all the chicks from hatching one at a time which would be impossible to deal with.
If you don't have a rooster, but want to expand your flock the easiest way is to buy fertalized eggs from a local farm or online. Any place that has a rooster has fertilized eggs. It also doesn't have to be the same type of chicken. They tend to even lay on duck or quail eggs!
Let the hen go broody by providing her with fake eggs, but only if you can get the fertile eggs under her within a couple days. You don't want her having an extended brooding period, as the brooding is hard on their little bodies. Let her sit on the fake eggs and don't disturb her. When you go to introduce the fertile eggs there is a number of ways to do it.
This page contains the following solutions.
A good thing a brooding hen can do for you is raise some new chicks. You can buy some hatchlings, and put them under her in the evening. She will take full responsibility for food, warmth, and safety.