Hypoglycemia is an insidious condition that can show up as symptoms of depression, anxiety, mood swings, fatigue - general unhappiness. It is good to read about this, because diet will correct it and return enthusiasm and well being to some individuals, without further complication.
Not that any of the above symptoms should not be investigated along other ideas, but in the spirit of keeping things simple, it is useful to get some knowledge about hypoglycemia. If it is present, the other remedies are not going to work well anyway.
I know ballet parents want to do the best they can for their dancing children...read an introduction to hypoclygemia and see if it applies to your dancers.
I highly recommend The Perfect Pointe Parent's Manual for more about disordered eating and other dance parents worries.
