Others have already spoken of Labs and Goldens as wonderful service dogs. Another great service dog is a German Shepherd. Again, a larger dog. They are very smart and easy to train. They are also very loyal and protective of their master and family. If your daughter spends a lot of time alone in the house, this might be a very desirable trait.
Larger dogs do eat much more than their smaller counterparts as puppies. But as they grow older, they tend to eat about the same. I have a 7 year old 80 lb. Redbone Coonhound and a 50 lb. bag of dry dog food (