Are these actual black-out or "I stood up to fast"? I used to get them more frequently when I was having problems with hypoglycemia. These days, not so much. Is she eating enough fat? Is she still eating a lot of carbs and starches? Not enough? Are you two IFing? It can take a while for the body to start efficiently using fat for energy so her blood sugar may be out of whack. Women sometimes need a bit different macro-nutrient levels. Or she may have different issues. If she's eating enough and getting enough fat then it would probably be a good idea to see a doctor, at least to have bloodwork done to see if she's possibly anemic or something else.
It could also be carb-flu. Not sure if the "mini black-outs" is part of it, as I never really had it due to changing my diet gradually, but someone else may be able to weigh in on that.