Take her to the Hana Hana Room untop of the Sheraton Wikiki. Dinner, wine, dessert, etc. will set you back about $250, but she will never forget it. Best service and food around, every table has a great view of the beach and ocean, and they have a great dinner band and singer. We used to live in HNL and my wife still still talks about us going there for our anniversary.
Mark