I've posted this list before, HTH:
1. If she likes fashion, take her inside the original Chanel store and walk up and down Coco's staircase. Take a photo.
2. Go up to the top of the Notre Dame Cathedral with a sketch pad and have her draw the gargoyles.
3. If she dances, take her to the L'Opera Garnier for a tour and a stop at the gift shop, it's fantastic. Great ballet gear.
4. Go to the historic Shakespeare and Company English language bookshop. She can buy a book and they will stamp it with their imprint at the cashier. Kids books are upstairs.
5. Berthillon ice cream. Nuff said.
6. Take a day trip to the Loire Valley to see a castle or two.
7. Take a tour in a classic 2CV. I've done this, it is outrageously fun. I think there are a few companies who do this like:
http://2cvparistour.com (actually, I've done each of these with my DD).
8. Get tickets for the Eiffel Tower and take the elevator up but WALK BACK DOWN. It's an amazing trip inside the skeleton of the Tower.
9. Go to Les Halles and buy cheeses and charcuterie for your own French style meal.
10. Go on a scavenger hunt at the Louvre (again, there are companies that do this).
Have fun! Jealous!