First off, congratulations on planning your trip to the Walt Disney World Resort.
With the Disney Magic Your Way ticket, you certainly can add days on to it. As long as you add on within 14 days of the first use of the ticket and have at least one unused day left, you'll be fine. Just head on over to any ticket window at the parks, Guest Relations at Downtown Disney or the Concierge in the lobby of your resort.
Take a look at the information on
Tickets & Passes, including some frequently asked questions if you'd like even more information.
Your daughter may surprise you. In my own experience, my kids were always raring to go in Walt Disney World at that age!
I wish you a MAGICAL vacation, Carla!
-Jacqui