Thank you guys so much for your helpful suggestions! I just got off the phone with Vacation Planning.
Here is what we were able to put together:
I booked a reservation for the Ariel's Grotto Princess Character Breakfast. The are going to get an autographed photo of Ariel and create a card (signed by Ariel) inviting her and her family to have breakfast with her. It will provide the reservation information. They will have all of that for me at check-in. It will be packaged in a white envelope and will include Celebrating buttons for each of us.
Then, on Thursday afternoon, they are going to deliver a little package with Princess Ears w/her name embroidered, and some other treats will be included with that. There will be a card that says something to the effect of: "We are so proud of you! Love, your Disney Pals." (Cost of this was about $50).
She is going to flip!!!