Hi Shiela,
Your magical vacation starts in just a few weeks. How exciting! But I can imagine how you are feeling right now trying to get your niece to tag along.
I had this exact issue a few years ago. My wife and two boys had everything planned out to spend Christmas at Walt Disney World Resort. And then my cousin from Argentina was coming over to visit. It took a bit of Pixie Dust and help from Guest Services, but in the end, we had a magical time.
Since all Resort hotels can fit a family of four, that part is taken care of. Next is to see if you booked your package as part of a
Special Offer. If so, there might be availability issues, however you want to contact a vacation planning specialist at (407) 939-1936 (or your travel agent, if you used one) right away to add your niece to the reservation.
Finally, dining reservations. The good news is that you can use the
My Disney Experience mobile app to quickly see availability and modify reservations to add an extra Guest. This could be a challenge for some very popular places, however keep checking. Many Guests change or modify their reservations before arrival up to three days in advance. In my case, I was able to book a dinner reservation for the five of us, on Christmas Eve, at
Be Our Guest Restaurant, two weeks in advance.
Sending Pixie Dust your way...
Ricardo.