Anything 'beauty' related - manicure/ spa, etc.
Going for a walk.
Going somewhere different (e.g., walk on the beach).
Watching a movie at home/ cinema.
It's tricky, as you've said you're not in to the outdoors, so all I'm coming up with are food/ drink related stuff indoors!
You could always say that you'd love to see her, and she could come over and hang out one evening instead.
I suggested coffee/ cake as they're quite low key things that don't take too much time or effort. Most of the 'day out' things take a bit more time, and if you're not keen then that's stretching it out for longer.