I've read alot about dogs and dog care from books and online, but I I'm not a vet, so I may not know what I'm talking about. I can't vouch for everything I think I know, especially since some of it may have come from irreliable sources and/or old wives tales, but for what it's worth (which isn't much):
I would think it really has to be either pee or drool, because dogs only sweat through their paws, and the amount of wetness your describing, it would seem unlikely to be sweat and almost as unlikely drool (if she were a mastiff breed known for drooling, like a St. Bernard, Newfie or Rottie, I'd be more inclined to suspect drool, but I would guess that if it was a drooling problem, you'd notice it during the day too, but maybe not).
That it doesnt' smell like urine makes me think it might be very diluted urine - do you ever notice her drinking more water than usual (or could she be drinking from the toilet or another source of water without you realizing it).
I would be concerned that it could be a kidney problem, diabetes, or some other health problem. It could be serious, so I think a vet visit probably would be the best route, just to be safe.
Last edited by kaplods; 10-11-2009 at 12:39 PM.