Okay, I'm noticing not a lot of local people answering you, but I agree with all their answers and thought I'd offer my advice, too. :) LOCALLY (I'm not far from you in Bolingbrook!) I buy our rice milk at Meijer, it's also at Jewel. Refrigerated rice milk is "near" our milk section at Meijer, but closer to all the creams for coffee and such, and there's soy milk there, too. It's also at the BOTTOM of the whole refrigerated section- they really don't make it easy to find! Unrefrigerated boxes of rice milk (costs more!) are with the evaporated milks at Meijer- in the baking aisle, also towards the bottom. Go figure. :)
Jewel also carries rice milk- I think it's in their "healthy/organic" type of section. Trader Joe's and Whole Foods are also places to look. You can even get whip cream made with rice milk for the holidays at Whole Foods! (just a fun random tidbit! LOL!)
Also, try cooking/baking with Fleischman's UNSALTED butter (green label on box) since it's made with soy and has no milk in it- it's just another way to reduce the milk intake for your daughter while you figure out what's going on. My son's allergic to milk, so I'm pretty familiar with all this! :) Let me know if you have other questions!