My son was actually allergic to milk, "outgrew" it, but then it became an intolerance. We had replaced all dairy with soy. Now, he is allergic to soy. I researched soy, and found out how messed around with soy really is, how the soy we consume in America, and the amounts, are not healthy. It is so highly genetically modified it is hardly food anymore. So between his soy allergy/milk intolerance, and that info, I pulled all soy derivatives/dairy from all our diets and we all feel better.
We replaced our milk with coconut milk and love it. I don't even like coconut. Still won't eat actual coconut, but love the milk.
As a mom who has done a great deal of food journaling to find food sensitivities, I suggest you find all the names for milk/dairy (casein, whey, etc), start reading labels VERY carefully, pull them from her diet, and keep a record of what happens. After 2 weeks, let her have some milk and see what happens. That is the best way to tell what works for HER. An intolerance won't usually show up on a medical test.
I like the book "The Prescription For Nutritional Healing" available from amazon for info on food sensitivities/allergies.