Is it really hot where you are?
It is not good that she leaves the nest for hours. That is showing fickleness on her part (which is often problematic in commercial quality BO, they don't have good brooding genetics being selected for egg production).
However, I have had numerous mishaps on nests that left them unattended for a number of hours and still had some hatchings. It does cut down on hatch success. Generally I get a 50% hatch rate if there has been neglect.
So it's worth a try. You might attempt to block her into the nest better so she doesn't get distracted foraging with the flock. If she just has a small area to eat, drink, and take care of her needs, she may be more inclined to attend to her nest....or panic if she can't get out. I personally have not had good luck with BO brooding for this very reason.
LofMc