Those are ALL really good suggestions. If you think the day spa idea is a good one (and it sounds good to me, or half-day, or mudbathseaweedwrapsaltscrubmassage coupon or something similar -- or maybe there's something she'd like to go see? film, play?), you could make it extra-refreshing by being "proactive" and helping to make time for her to actually USE the coupon -- include your own "coupon" with available dates and times for her to go while you mind the baby (or arrange for someone else to if your gift is a date for the two of you) or plan to pick her up with dinner afterwards...
Sounds like she doesn't put herself first, so it would be a real gift if you make sure it happens!