The best way to get from park to park is via disney transport (motor coaches, ferries, monorails).
Be sure to go to go to both of Disney's Water Parks, Blizzard Beach and Typhoon Lagoon, as well as the Downtown Disney area, where your sister will absolutely love the new Once Upon a Toy store and your entire family will love the World of Disney Store...plus there are other shops and eateries there. Be sure to visit DisneyQuest (indoor "theme park" with tons of interactive games) and you might like Cirque du Soleil: La Nouba.
You may also wish to experience one of disney's two miniature golf courses, Fantasia Gardens, which is within walking distance of the Dolphin, or Disney's Winter Summerland next to Blizzard Beach.
Furthermore, try touring some of the other Disney Resort Hotels if you have time (especially Disney's Animal Kingdom Lodge if you like animals).
The Dolphin is a beautiful resort so I'm sure you will love it.
As for attractions, your sister can go on everything except Rock 'n' Roller Coaster Starring Aerosmith and Primeval Whirl...have her wear big shoes if you want her to go on Rock 'n' Roller Coaster

Be sure to take her on all the classic attractions at the Magic Kingdom, including the Magic Kingdom Mountain Range. Also take her on the Tower of Terror, Test Track, Kali River Rapids!, all of Disney's 3D shows, Kilimanjaro Safaris, and Dinosaur. In all other cases, if it has Fastpass, go on it (pick up a park map and it will tell you fastpass attractions! Good rule to follow, although Pirates of the Caribbean doesn't have Fastpass, but certainly ride it. Also be sure to catch a few shows, The Great Movie Ride, the Studios Backlot Tour, and the ExtraTERRORestrial Alien Encounter, Festival of the Lion King. Oh...and see all of the parades! The best ones are SpectroMagic, Mickey's Jammin' Jungle Parade, and the Share of Dream Come True Parade. Also be sure to catch IllumiNations Reflections of Earth, Fantasmic!, and Fantasy in the Sky.
Actually, I'll be nice! Here are all of Disney's Fastpass Attractions:
Disney's Animal Kingdom Park:
Kilimanjaro Safaris
Primeval Whirl!
Dinosaur
Kali River Rapids!
It's Tough to be a Bug!
Disney-MGM Studios:
The Twilight Zone Tower of Terror
Rock 'n' Roller Coaster Starring Aerosmith
Star Tours
Indiana Jones Epic Stunt Spectacular
Who Wants to be a Millionaire--PLAY IT!
Jim Henson's Muppet*Vision 3-D
Voyage of the Little Mermaid
Epcot:
Living with the Land
Honey, I Shrunk the Audience
Test Track
Maelstrom
Magic Kingdom Park:
Big Thunder Mountain Railroad
Splash Mountain
Space Mountain
The Haunted Mansion
Jungle Cruise
Peter Pan's Flight
Buzz Lightyear's Space Ranger Spin
The Many Adventures of Winnie the Pooh
That just about wraps this up! Consider taking your sister to Mickey's Toontown Fair--take the Walt Disney World Railroad back there

Have a great trip!