A.,
In this battle of wills, ask yourself why is it a battle? She is getting plenty of nutrition as you said. Instead of making food a control issue, which can affect the way she looks at food forever, try easing off a bit. I know that you want her to be an obedient child, and there is alot to be said about letting your toddler know who's boss. The last thing you want is to give in and have her think she can control you. But there is a balance here. My mother always said you can control what goes into your child's mouth, but not how much. The whole sitting at the table till your dinner is done only, in my opinion, makes a stubborn child more stubborn, and a parent crazy.
Let her know if she doesn't want to eat at dinner time fine, but she won't get anything until the next family meal, and stick to it. You can also try sending her to bed early, but not because she is "bad", try not to give negative associations with food. Once again let me stress that this can do damage down the road. You want her to have a positive attitude about it and think that she does have some say in how she feeds herself.
Hope this helps, good luck to you.
-K.