Dear L.,
Chronic congestion is definitely a symptom of a milk protein intolerance. My son had chronic colds and ear infections, plus a speech delay and a perpetually sad mood, as a result of just trace amounts of dairy in his diet. When we finally got him off all traces of dairy, he literally learned 50 words in a week, his mood brightened unbelievably, and he hasn't had an ear infection since. My son used to have sleep issues a lot like your daughter's, too; as soon as we got him off all dairy, he's been sleeping like a champ.
For soy milk, I go with the store-brand organic. At our local Stop & Shop, it's called Nature's Promise. This gets us away from genetically modified soy, which can have troubling health consequences if consumed regularly, but it's cheaper than a name-brand organic. I also recommend NOT going with a flavor, since they all have a lot of sugar and they give a child the impression that milk/milk substitutes have to be sweet.
You might also try rice, oat, or almond milk. The latter two are supposed to be the healthiest, but they're harder to find.
Best wishes,
Mira
P.S. If you think dairy may be the culprit, it's important to read all labels and get your daughter completely off milk and milk derivatives (whey, caesin, etc.) Companies are supposed to put allergins in boldface on the bottom of an ingredient list, so don't feel like you have to go back to school and get a degree in chemistry: just look out for "contains milk" at the bottom of the list. I know this sounds like a pain, but it's not that hard once you get used to it, and it results in a much healthier diet. I made my whole household dairy free when I got my son off dairy, since I didn't want there to be food in the fridge that he wasn't allowed to eat, and I lost 10 pounds :)