maybe try some soymilk or rice milk, the vanilla flavor as it may taste better to her and it won't cause the mucus that cow milk. Another alternative is goat milk. It's easier on her system than cow milk too. Really as all the others stated, we don't NEED to drink milk, The Dairy Board says we need it, but physically we don't. There are calcium enriched foods all over the grocery store.
Cow milk is originally meant from baby cows. Really, who ever thought, maybe we should drink the milk of other mammals. That is a strange concept now that you think of it.
Ovaltine, as the previous poster stated, is great because it's not just chocolate and sugar. It's actually better than plain ole chocolate. So mix that in some rice milk or soy milk and let her try that.--Good luck!
There are also flavored waters out there that don't have added sugars or chemical sweeteners. Some herbal tea might be good to, the kind made from fruits, like wild Berry zinger, etc from celestial seasonings. The kind w/out caffeine, there are tons of flavors out there, Then just sweeten it with sugar that you control-real sugar, not corn syrup and put in some ice.... That would be good too for you, keep you both hydrated in the hot summer.