Her body may be sensitive enough to know that some of the synthetic ingredients in the formula can't be processed by the body. This has happened with quite a few children I know. One solution is to grind your own baby food (health-food stores have inexpensive grinders). The Food and Drug Administration considers barley grass to be a complete food, one that is very healthy for babies. Again, it can be purchased at healthy stores such as Whole Foods or your local health store. The brand with the most nutrients is Dr. Hagiwara's and the organic one is best.
While it may initially taste a bit grassy to adults, children's taste buds are usually eat it. It can be blended with water or apple juice to form a paste, then mixed with room-temperature food, if desired. Most babies just eat it as it is. And you can use it, too, to help you get your health back after the pregnancy. You'll probably want to a teaspoon to about 4 oz of water and shake it in a jar.
I'm a prevention and wellness consultant specializing in natural health solutions.