My six month puppy won't stop drinking water?

She always has seemed to drink too much water, she gulps down as much as she can get but last night it was really bad. She was drinking so much, that she would completely ignore her food and when I finally pulled her away, her stomach was almost twice it's size and she felt like she was going to pop if I touched it. So I guess my question is: do either labs or Great Danes have a tendency towards diabetes? We also suspect a tiny bit of pit bull too if that helps. Can such a young puppy get diabetes? Is it normal for a big dog to drink that much water? What can we do to keep her from hurting herself? Could the lab in her just be obsessed with water? Sorry for such a long post, and I really appreciate any help