Hi Patrice!
How exciting that you are visiting Walt Disney World with your sister for her first visit!
When you arrive make sure to ask for the complimentary "First Time Guest" button for her. You really can't go wrong with any of the parks, as they all offer something special and fun for everyone!
Epcot is a wonderful park for adults, as there are so many wonderful things to do and see. You both can dine around the World Showcase and enjoy flavors from around the world. While you are touring the World Showcase you can also go shopping (I particularly love the shop in Japan) and see wonderful shows (I love O'Canada).
You also won't want to miss
SeaBase, which has a huge aquarium with over 4,000 species.
There are also loads of great attractions, such as
Test Track,
Frozen Ever After and Living the Land.
At night you will love watching
Illuminations.
I hope you both have a magical vacation!
Magically,
Stacy