At this point, I would not be concerned about the specific cause, but continue with the treatment on all fronts, and be glad they're working. Yes, it may just be one of the factors, but it's quite possible that it could be a combination of things. Being so selective with her foraging may not have provided a balanced enough diet, so she was somewhat depleted in vitamin D, which was exacerbated when she began going broody. No matter, now you know what to do, and that's the important part.