L.L.
I can guarantee you that switching her to a healthier diet did not cause this behavior. There's only a little evidence that this kind of diet works for autistic conditions, but I highly suspect that it's because most of the foods you end up eating on this diet are free from chemicals, additives, and most importantly food coloring, which has DEFINITELY been linked to all kinds of crazy behavior.
Something is probably causing it, but I just don't think it'd be the diet. I hope you can figure it out!