I think I would just monitor her and move her to ground after the chicks hatch. I personally have not had luck relocating a broody but I know others who have. If they are in the hay barn, most likely they would just tumble down and be fine. I am amazed at how "rubber" little chicks are!
X2, if she feels safe and content there then let her do her thing. You can figure an approximate hatch time and watch for chicks. If you see her off of the nest with the chicks in the loft then help them down if you feel they need it.