H., My pediatrician suggested first of all waiting until after a year to introduce milk, it can lead to an increase cancel of allergies. Also, as a baby until between 2 and 3 yrs (depending on who you ask) your daughter NEEDS to be on whole milk or a whole milk substitute, such as enriched rice or soy milk. The fat in this milk in necessary for proper brain development, your child will not get fat from whole milk before 2-3 yrs old, if your child does start to have a weight problem, cut out other fats, use leaner milk, limit junk food, etc. You can ask your pediatrician about the importance of whole milk or here is a website that discusses some of these points. http://www.nlm.nih.gov/medlineplus/ency/article/002448.ht...
Also, some children can be allergic to milk protein (whey) or they can be lactose intolerant, which could be causing your daughters problem, but most likely her digestive track isn't ready to tolerate the proteins in cow's milk or soy milk. If you want to start introducing dairy, try cheeses and especially yogurt, because that has enzymes that help break down the protein in your child's digestive track. Some information on cow milk or soy protein being hard to digest under a year is also in that above link. Introducing easier to digest dairy can help her system learn to break it down without discomfort. That's why formula's and breast milk are so good, the proteins are broken down for the child. Good luck and feel free to contact me if you want to talk further.