A few ideas:
1. You could book an early breakfast at Crystal Palace in MK before the park opens, so then you get to go into the park before the crowds are there - that way you get to walk down Main Street and see the castle while it's quiet and mostly empty in the park.
2. Depending on where you're from (especially if it's from somewhere outside of Florida), it might be special to do a water sports experience - rent a jetski, go parasailing, rent a boat, go tubing/waterskiing. Wilderness Lodge has the Teton Boat & Bike Rentals station where you can get everything set up. I believe the Contemporary Resort also has a place where you can do water sports, as well.
3. Magic Kingdom has a Fireworks Dessert Party at Tommorrowland Terrace that can be booked ahead of time. There is a dessert buffet and seating to watch that evening's Wishes.
4. In Epcot, you can try one new treat from each of the countries around the world.
5. If you get to the park super early in the morning, you can make it to "Rope Drop" when the park opens and see the special little show they put on in front of Magic Kingdom as it opens.
6. Pick a Pearl in Japan at Epcot - This is something a lot of people enjoy, and it gives you something special to take home with you and keep as a unique souvenir. You select an oyster from a tank, and the cast member opens up the oyster to find a pearl inside. The pearl is yours to keep as it is, or you can have it set into a jewelry setting so that she can have a special ring or necklace to take home from her trip with her Disney pearl in it.
7. A lot of times people end up focusing only on their favorite rides each time they go. Maybe on this trip you can try to see the shows or attractions that you haven't caught in the past. One of them could end up being her new favorite!
It sounds like she will have a very special time simply because you are planning it for her.
Hope you have a great trip!
