Guess it depends on what is important in your house. I have no problem if my kids don't want to finish their main meal - it doesn't mean they don't get something else later on if they want it. As far as understanding, well I'd say she knows the routine, but that's probably it - but doubt very much that she has the same adult interpretation that you do as in "only when I finish all my main meal am I allowed to have dessert" if that makes sense? My ds at 3 would understand this concept, but not my 16mth old.