Sometimes mine would skip a day... Trust me, I have yet to hear of a broody dying because she was so determined she wouldn't leave the nest at all... My BA did lose alittle weight but once the chicks hatched she was up and fine.. The Java did great the first time around but has lost alittle the second time, I expect a little, its hard work and no they aren't up and eating as much as they normally would but what they do eat sustains them, Nature is a wonderful thing when we as humans allow it.. we do more damage when we think we know better and intervene.
This broody is pretty hefty, so a little weight loss hopefully won't hurt her.