my broody hens always become very aggressive when they become broody. The growl and puff up at everyone. The layers try not to look at her, come in and get in another nest, do their business and get out. Even if she was lower in the pecking order, she rises as she broods.
The only time I worry about is the 12-15 hours of hatching. If the first hatched chicks get out of the nest, and she is still setting, trying to get the later eggs to hatch. At that time, I lock the layers out of the coup, and give them a nest out in the run. But once she has them hatched, I let the flock back in. And I think the hen claims the chicks longer too. Right now, I have 11 seven week chicks that still follow the broody hen around, and she still talks to them, and several of them still roost right next to her, a few are a little distance away.
Works for me, my grandfather was an old time rancher, and once told me, never forget that she knows more about being a cow, than you ever will. And I think that applies to chickens too. I do best when I interfere the least.
Mrs K