My 3yr old grandson is going through a similar thing, He eats well and I think healthily throughout the day, ie he has porridge or cereal for breakfast and has a sandwich, grapes and yogurt for lunch. But, he doesn't very often eat his evening meal. I have said not to worry because most psychologists will say that a child will eat when hungry and no matter what the reason, I don't think he will starve. His mummy has not long gone back to work after taking maternity leave following the birth of another son and nursery hours have changed. I think there are lots of mixed reasons and of course it is one of the things they can control and we cannot make them do. I would say unless your granddaughter is drastically losing weight and is becoming poorly, try not to worry, hopefully it will sort itself out. Easier said than done I know sometimes.