Personally I like the idea of candles, maybe some fondue and a chick flick... or perhaps some chocolate to dip strawberries into while sipping champagne... whoops
Sun setting on the Thames, a warm summer night, soft tunes playing, a little wine, cheese and fresh bread ...
Kidnap her for a day to be a tourist in your own town, or area. As I remember there were lots of free attractions to visit. Perhaps create a tasting afterward of something she especially likes.
After an esp. stressful day greet her at the door with a rose or something similar. have a tub ready to be climbed into... and offer to wash her hair.