Do you have a car? If no, then I would spend time visiting the resorts, maybe play a round of miniature golf or two, Downtown Disney and West Side, and take the boats all over the place. Particularly between Port Orleans Riverside and Downtown Disney, and the small ferry that connects the 7 seas and bay lake resorts. These later are especially great at night, when there is a full moon going. At Fort Wilderness there used to be a long boardwalk east of the resort (walk along the beach away from the Magic Kingdom, it's back there) but I don't know how it faired there last couple of years. But as Slappy said (I couldn't resist!) maybe your girlfriend wants to just spend a day at the pool.
If you have a car, I might suggest getting away from the parks for a day. Drive to Downtown Orlando, and in particular Thorton Park by Lake Eola and stroll around. Hunt down Dickson Azalea park for a nice little stroll. Or, head up to Winter Park, stroll around, and take one of the boat rides through the lakes and the canals that connect them. For Dinner, head off to Press 101 up on Dr. Phillips Rd. (off of Sand Lake Road) which is a weird combination of pressed sandwiches and a wine bar, with excellent soups.