You know what, I wonder if belling her is out of the question if this becomes a recurring problem? A jingling bell caused by her walking beside the bed would probably penetrate the sleep fog enough for you to notice and run her out. Unless she moves around at night alot... then you'd just be annoyed.
I taught a pup to ring a bell hanging from the door, but I doubt an arthritic old dog is going to be interested in learning that.