There is a chance of failure, and there is a good chance of success, and IMHO it is the only way to raise chicks! I will never go back.
If you have a small nest, or a hen with a good Broody attitude, so that other hens do not lay in her nest, mine layers tiptoe past my broody hen, and try not to look at her for fear of upsetting her.
you can leave her where she is.
If you want to move her, move her first putting her on golf balls to see if she will stick for a day or two, while you round up some eggs. Then at night, in the dark, slip the eggs under her.
The real thing is you want to put all the eggs under her at the same time. So they all hatch at the same time, and then call your feed store and see if you can get some more chicks at that 21 day hatch date, in case the eggs don't hatch.
I am on day 5. It is the longest 21 days ever!
Mrs.K