Disney is a great place to get over your fears!
I would suggest at the Magic Kingdom:
Jungle Cruise (at night, if you can!)
Pirates if the Caribbean
Splash Mountain (the ride is so imaginative and wonderful, it is a shame no to do it for fear of the last drop, or getting wet). To me, it is one of Disney's finest!
Haunted Mansion
Peter Pan
Small World
Winnie the Pooh
The Cinderella Carousel
Buzz Lightyear
Tomorrowland Transit Authority
Carousel of Progress
Epcot:
Test Track
Maelstrom
Journey To Imagination (DD loves this)
Take her to see Turtle Talk with Crush at the Living Seas, definitely... it is AWESOME, DUDE!
Ellen's Universe of Energy
Not a favorite of mine, but many others love it--- Spaceship Earth. Also, make sure to have a nice lunch or dinner in one of the countries in the World Showcase!
Soarin', if it is open when you go!
Disney MGM-
The Great Movie Ride
Voyage of the Little Mermaid
Backlot Tour
Indiana Jones Stunt Spectacular
Muppet Vision- 4D
Beauty and the Beast, Live on Stage
and if she is REALLY brave... Tower of Terror (talk about overcoming that fear of heights)
Animal Kingdom-
Kilomanjaro Safari
Kali River Rapids (but she may get soaked)
Don't miss Festival of the Lion King!
Hope Grandma has a great time overcoming her fear of "Flying"!