Hey Jessica! I have a six year old daughter who loves Walt Disney World, your niece is going to have a great time.
Since you are visiting in late November, I suggest looking into Mickey's Very Merry Christmas Party. It is a hard ticket event that runs select nights in November and December. The party starts in the evening and you can enjoy complimentary cookies and hot cocoa while strolling down Main Street, U.S.A watching the snow fall. During the party there are special character meet and greets, dance parties, a special parade and a holiday firework show. If the dates work for you, I highly recommend it.
Something my daughter never skips is a trip to the
Bibbidi Bobbidi Boutique. The Bibbidi Bobbidi Boutique is a special salon for little girls where they can be transformed into the princess of their choice. It is a magical experience your niece would probably really enjoy.
A few dining options to look into are dinner at 'Ohana, breakfast at Tusker House, Cape May Cafe, Sci-Fi Dine-In Theater, Chef Mickey's and 1900 Park Fare. Those are all great places that your niece is sure to love.
I hope this gives you a few ideas for your trip, feel free to ask if you have any other questions! Happy planning!