Whisk her away to New York on a redeye flight, hit a broadway show, nice restaurant, maybe a site or two and shopping the next day, with a whirlwind trip back home. Crazy, spontaneous, fast and furious, and a great memory.
Or...if that is the range...flight to Florida, do the scuba/snuba excursion where they give you a 30 min lesson on breathing through the air hose etc...go snuba'ing in the tropical waters with fish, rays, etc.... beaches, shopping, relax etc....