Hello Devarn! Thank you for bringing your question to planDisney.
During the reopening period of Walt Disney World Resort, the
Disney Park Pass system was implemented to manage theme park attendance. At this time, all Guests ages 3 and up will need both a Disney Park Pass theme park reservation and an
admission ticket in order to enter a theme park. I have been keeping an eye on the
theme park reservation availability calendar, and I know that some upcoming dates have limited reservation ability. I do see that as of this writing, Disney Park Pass reservations are not available for
Magic Kingdom Park on the date you plan to visit.
One unfortunate aspect of the Disney Park Pass system is that it is harder for Guests to make plans to visit Walt Disney World Resort in the near future or make last-minute changes to their plans. I wish I was able to wave a magic wand and save the day, but I am sorry to say there is not currently a way to add your niece to your group reservation. I do advise you to keep checking; other Guests' plans change all the time and it is possible that a reservation might become available. It is not necessary for everyone in your group to be on the
same reservation -- as long as everyone in your party has a Disney Park Pass reservation for the same theme park on the same day, you'll all be able to enter the park together.
One idea I have for you is to upgrade your tickets to include the
Park Hopper Option. Some (or all) of your party could go with your niece to a different theme park that has Disney Park Pass availability, and then after 2:00 pm when park hopping hours begin, join the rest of the group at Magic Kingdom Park. My only other suggestion would be to change the date of your visit to a later date when Disney Park Pass reservations are available at Magic Kingdom Park for your whole group.
Devarn, I know that is not the news you were hoping to hear. I will be wishing upon a star that some pixie dust flies your way and you will be able to find a solution that works for your group. If you have any additional questions, please feel free to stop by planDisney again anytime.
Anne Marie