I have had this happen. My chickens do have a coop but during the day I free range the chickens and I have had on 2 occassions a hen hatch chicks in the pig and llama barn hay loft. Scince it is such a large drop, and also little chicks will fall between hay, I would do something about it. Here are the things I did when I was in your situation:
-took one egg at a time from under her, at night, and candled and marked them, putting them back one by one.
-made sure I safely placed her and the eggs on the floor of the loft and not on top of bales of hay.
-started feeding a bit of chick starter in with her feed as she may loose weight while sitting on eggs.
-Most importantly-Placed a cage top over her.
There are 2 main worries when they hatch in a hay loft.
1-the chicks will get hurt from falling, stuck between hay bales, etc.
2-the barn cats, wild animals, or even other chickens may kill the babies if they get the chance.
I would definitly place the top of a cage over her.
Good luck, I have had 2 very successful hatches in a hay loft.