Any chance she could be sensitive to nightshades? It's the only thing jumping out at me. Maybe not enough carbs? It's all I can pick up on.
4.5 is tough. Actually I think each 1/2 mark is tough, i.e. 18 months, 2 1/2, so on. The resistance and regression is often a hallmark of a developmental period. Like fussy babies trying to crawl or walk. Mine always seem to get impossible just before they either leap forward or get a cold (go figure!).
I hope tomorrow is better!