A.B.
Hi D.,
At eight your daughter should be old enough to understand the basics of nutritious meals and the food pyramid. If she hasn't already studied this in school, there is a "for kids" section in the US Agriculture website that you can use to give her the basic information (http://www.mypyramid.gov/kids/index.html). Make her responsible for planning out her food menu, to include snacks and breakfast, within guidelines you can stand. For example: she needs to have at least two servings of fruit, three of vegetables, no more then two of the same main courses in a week, a limit on dessert type servings/daily calories, or whatever else you think is reasonable and necessary in your household. Sit down with her the day before you go to the grocery store and tell her she needs to come up with her menu for the week (hopefully it will be stuff the whole family likes -- and if you need to make that one of the parameters, then do that up front too), so that you can get the ingredients the next day. Tell her that you are not making two dinners, and if she insists on eating something that nobody else likes, she will be responsible for preparing it as well. Actually, this might be a good opportunity to get her interested in helping you out in the kitchen and learning how to cook in general.
I'm personally not a big fan of forcing kids to eat things they don't like. Encouraging them to taste new foods is one thing, but I think meal time should be a pleasant/bonding time experience for all participants, and not the best time to have battles. Besides, as adults we have certain preferences (I don't like Mexican or very hot and spicy foods) and would resent somebody who tried to force you to eat it anyway. I think that if you transfer the responsibility of the problem to her: selecting, preparing, and eating nutritious meals that aren't a lot of extra work for you, that you will find that she'll eat what she picks and dinner times will become much more pleasant. Also, she will learn a lot about nutrition and hopefully learn to appreciate how much work you've done in cooking and planning meals for the family.
Best of luck,
A.