A hard stomach and gas is not a good sign. When was the last time the dog took a poo?.

What could be most wrong is that you haven't yet called your Vet! Does your dog have access to Rawhide chews? (This could be an impaction of the rawhide in the intestine or bowel, that is starting to turn toxic...and if left untreated, could kill your dog.) Is there ANYTHING you can think of that your dog may have gotten access to in abundance....that is something the dog simply stuffed herself on? For Example: Hannah once got a hold of a WHOLE pizza...granted we found out she DID hide several pieces of it, evidently for "later snacking" (she must have realized that even SHE has limits), and so in typical Husky (Hannah is a Shepsky) fashion, put some of it away for later! She was bulging on both sides, her stomach was hard...packed to the gills so to speak. And eventually, she did start farting...horrible smell and as if there was a putrid green cloud hanging over her as she lay, trying to sleep it off next to me in the office....ugg THIS might not require a Vet visit...she lived through her gluttony...although I did think I might keel over from the stench...and when she started accessing her little stock pile (which WE could not locate at all, looking under ever piece of furniture in the house, including behind the piano, even though no way could she manage to get back there!) I thought....you gotta be kidding me...you are still swollen as a tick here, (remove pizza from dog's maw and chuck in trash can...) The problem here is it could be nothing to worry about IF YOU STRONGLY BELIEVE....HAVE PROOF...(MISSING PIZZA) THAT YOUR DOG OVER INDULGED.... Then again...this could be a life threatening situation that you need to take immediate action if you hope for a happy outcome! A twisted stomach, intestine, or bowel, or God help us BLOAT....is LIFE THREATENING...and not a one of us can see YOUR DOG, or check her for vital signs....CALL YOUR VET unless you are sure she just ate too much of something NORMALLY SAFE IN SMALLER AMOUNTS! If this is a large dog....with a DEEP CHEST... it could be BLOAT...and in that case, the clock is ticking fast...call the Vet NOW.

Take her to the vet.