It's the combination of Essential Amino Acids...
Traca is right...you have to make sure you combine one from Column A with one from Column B... If you can always think to make sure she has either a meat animal protein (milk, egg, cheese, or the like), or a combination of a legume AND a grain product. That could be as simple as peanut butter on whole (stressing WHOLE here) grain bread. Beans and rice are a great combination...but beans and cornbread are equal to that. Corn is a grain product. Peas, beans, peanuts, and soy...all are of the legume family. You can also combine either of the two with vegetables to get the same result, but you have to seriously know your veggies. I got caught up in this when we lived rather essentially in the mountains. I never knew when we'd be stuck due to weather and not have the opportunity to shop for fresh food.