I am an advocate of leaving them with the flock. If you remove a broody hen, she loses her pecking order, and when you reintroduce her, she has that fight.
Where as if you leave her, she generally rises in pecking order, and EVERYONE gives her space. When the chicks are hatched, she will naturally place herself between the chicks and the other hens. She will defend them vigorously if a chick strays too close to a layer and gets pecked. The chick learns quickly to stay on the 'right side of mama.' And by the time she leaves them, they have been accepted by the flock.
The tricky part can be day 20. Sometimes it can take several hours for all the chicks that are going to hatch to hatch. And sometimes those early chicks, will get adventurous and go explore the world while the broody hen is still tied to the nest so to speak, and the layers can get them, and they won't be nice. Once the clutch has hatched it, there is no problem, as the broody hen will take care of it.
So what I do, is very early on the 20th day, I lock the layers out of the coop. I put some kind of nest outside in the run for their needs, and my runs have a roost, so they just stay outside. Often times, eggs under a broody hen can start hatching on day 20. 12 hours later, I let the layers in again.
Now my broody hen has always picked a nest to brood in. I leave her there even though it is a couple of feet off the ground. Once the chicks hatch, she has always moved to the floor, and created a nest on the floor of the coop for a couple of weeks. When they are a couple of weeks old, she has moved them up on a board to roost. By having a board at roost height, I think she stays interested in them longer, as she is not fighting the urge to roost.
I am praying for one, I generally get one about now!
MrsK