Could be GERD, Could be simple reflux, Could be latose intolerance (that's an easy one), could be celiacs disease, could be a sugar intolerance.
Basically could be alot of things.
A good GI workup she pry needs if she is throwing up for no reason. If you want to try something else first I would elimanate ALL dairy from her diet... regardless if you think she handles certain things well or not. Maybe she doesn't. Maybe that stuff doesn't digest and sits in her gut sometimes all day and night till she pukes. Hard to say. Elimanate it all for a month. Replace it with calcium fortified oj and soy milk (doesn't taste much differnt), replace cheese with rice or soy. replace yogurt with soy yogurt. You get the idea. I did this for my daughter who had the same problem as yours and she's been fine now for nearly a year. She just can only handle dairy in VERY small doses. Basically once a week or she's all messed up.
You could also elimate all gluten from her diet (this can be hard) to see if it's celiacs disease. It's real commen anymore and basically several kinds of grains they just can't handle. You could try that if you still didn't have luck with the lactose.
After that if still no luck I'd take her to a gi. She might have gastroparesis or GERD or just simple reflux. There are meds that can fix that. She could even take a reglan before bed and that would calm her stomach and force it to digest if needs be. Otherwise a simple rantidine could help or maybe even a Proton pump inhibitor (prilosec, nexium)...
But if she was my little girl I'd take her to a GI doc and let her get a work up. Something isn't right.