Hi David!
This is such a sweet question, no pun intended! Disney's Caribbean Beach Resort has always been one of my favorites, so I know just which little dishes of pineapple upside down cake you are talking about. I might not like them quite as much as your mom, but they are delicious!
It's tough to tell where on Walt Disney World Resort property will have the exact same cakes, but I know of a few places where I am sure I have seen it offered or have found it on the menu and I'm happy to share those with you below. I certainly hope you are able to cure her pineapple upside down cake craving on your upcoming adventure.
Disney's Pop Century Resort - We stayed here a trip or two ago and I remember seeing single-servings available in the food court.
50's Prime Time Cafe or Tune-In Lounge - Both of these offer a pineapple upside down cake on their menu.
Yak & Yeti Restaurant - I've tasted this delicious option too, and it's served warm with vanilla ice cream and a gooey caramel sauce.
Have a wonderful vacation, David, and please send us another question if there is anything else we are able to assist you with.
Magical Wishes,
Lauren