K.S.
I don't know if children can develop the "allergy" out of nowhere, but I have heard that they sometimes cycle in terms of intensity. Perhaps, it's always bothered her, but not enough to notice or to mention? I just found out my 2 yr old son is lactose intollerant as well...mom diagnosed. :) He kept spitting up yogurt with peaches, so I thought it was the peaches, then it was with strawberrys until finally it dawned on me that it might be the milk. He had been fine for the first year and a half, but did have some reflux issues. He also was on Previcid, but after I figured out this intolerance thing, we've been able to go off the medicine! That was my whole goal...yes it's a little difficult, but switch her to soy milk or rice milk instead of cows milk...you might want to try vanila flavored first if she's picky. They also make soy yogurt that tastes really good and fruity. We don't let him eat cheese, and we limit his butter on his toast. Smart Balance WITH FLAX OIL Butter is the only one without milk. They also have SEVERAL cookbooks online and in the stores that offer milk free cooking. You can still make cookies, cake and all the other crazy things she likes, but limiting her milk intake. Iron Kids bread is the only bread without milk products also.
Let me know if you have any questions. Hope that helps. It does sound like an intollerance problem.
K.