I have thyroid problems along with vitiligo as well and have had for many years, the only time I have ever seen any improvement with this issue was on a strict vegan diet. Lots of juicing and the like. I am suspecting gluten as a major force in this issue. If I stick to gf foods, brown rice and loads of vegetables and the like, my skin looks free of it (only I know it's still there ever so light that the avg person won't see it)..then all of a sudden I feel brave to eat some thing I should not have and the next day there it is. The one thing to keep in mind is that this is an autoimmune issue...the body has something it is exposed to or taking in daily that makes it worse. You can get it cleared up to a certain point, it may still be there but ever so lightly..then again it may go away entirely depending on her overall health. I wish your daughter luck on this issue.
BTW, on the struggles with fibro, have you thought about going off meats, nuts and olive oil...just for a good three months. It's worth a shot. (if you haven't yet, check out Dr Gerson's Therapy at youtube. There is a woman who had fibro severe...those three foods you are eating are not allowed on therapy the diet...so it's just a thought)