Build, buy or borrow a broody buster. A broody buster is just a simple wire cage that you place the broody hen in. I use a wire boxtrap that I have around. You could build a simple one with chicken wire and scrap wood. Broodiness is a hormonal thing with some hens. A lot of it has been bred out, but not all. If you are not going to have the hen raise chicks, then you will be doing her a huge favor by helping her get past the broody stage. It's hard on them to go through this, they don't eat or drink properly. they don't get out and get proper exercise. And they can stay in this condition for WEEKS. They can't help themselves, So it is a good thing to help her through this if you are not planning on hatching any eggs.
What you do is, put her in the broody buster for usually 2-3 days. Have the broody buster elevated so air can get under the hen. That's why it is important to have a wire bottom on the buster. Air HAS to get under the hen. You should put water in there, along with a little feed container. After 3 days, she should be back to normal, but if she goes back to sitting, back in the box for another couple of days.
I have 2 out of my 3 BOs that go broody kinda regularly. I just had one in the box this past week. She did a couple of days, and now shes back out enjoying the fresh air again. I'm giving some thought to maybe getting some fertilized eggs and put under one of them someday.
Jack