SHould I force her to conform to the Breakfast/Lunch/Dinner "Clean Plate Club"?

nope. there've been studies done that eating a little bit every few hours is better for the metabolism than big meals.

little kids pick at food. that's a fact.

as far as the clean plate club- i advise you to get away from the mentality. start a compost pile... then you won't feel bad about feeding the earth what you don't eat:)