Personally I let mine hatch with the flock and I’ve seen a broody get her chicks down from a 10’ high hay loft. Mama says jump and they do. A nest a little off the coop floor doesn’t bother me. I have moved broodies before, not to isolate her from the flock but because I did not like the specific nest she was in. Many people choose to isolate a broody. There is nothing wrong with that, just a different way of doing things.
I suggest you fix a predator-proof area with a fairly dark nest, food and water, and enough room for her to come off the nest to go poop for each hen. Fix it so you can lock her in there and no other chicken can get in. That’s her home for three weeks.
Many people let broodies hatch together and raise the chicks together without problems, but many of us, including me, have had problems where the broodies fight over the eggs or chicks with eggs or chicks being harmed. You can try it any way you wish but if I were doing it I’d separate them.
Build the nest so you can lock the hen in the nest itself. You don’t have to do it this way but I find it helps. Make sure the nest is not in the sun where it becomes an oven.
Take the hen off at night well after dark with as little light and commotion as you can manage. Lock her in that nest with a couple of fake eggs or expendable eggs. Leave her locked in that nest the following day until fairly late in the afternoon, then open it up, remembering to not let her out of that pen. She might come off to eat, drink, or poop or she might wait until the next morning. You are not being cruel to her. Broodies often go that long in between coming off the nests for their daily constitutional. They build up a lot of excess fat, especially in the vent area, so they can mostly live off of that while broody. That’s why they don’t need to eat or drink a lot when broody.
Once you determine the hen has accepted the new nest you can give her the real eggs. After a few days you can let her out of the pen if you wish, but you need to watch that she goes back to the new nest when she finishes her break. You may need to move her back. If you allow her out, you also allow the other hens access so they might lay an egg in her nest. This is the method I’ve used when I moved one but I marked the eggs and checked under her every day to remove any new eggs.
There are a lot of different variations of this. Different people are successful using different techniques, but I think this gives you a pretty good chance at success. Adjust it to fit your unique situation.
Good luck!