Hey, Michelle - you're from my home town!
The way the handled your mother's wheelchair in 2004 was not the typical way they were handling wheelchairs in 2004.
Since around 1999, in most cases the lines are accessible and people with wheelchairs/
ecvs wait in the regular line with all the other guests. That is called Mainstream Access (I put a list of the Mainstream Access attractions further down).
The attractions that don't have Mainstream Access don't have wheelchair access in the regular lines, so they have an alternate entry place.
It's possible that most of the rides your mom was able to go on were ones without Mainstream Access or (what we have found happens in the slower times) the CMs handled your mom when you came to the ride right away because it wasn't busy and it was easier for them to just take you in.
Even of the things listed as Mainstream, the "thrill" rides have the longest lines (and you won't be going on them anyway). Most of the quieter rides in Fantasyland have wheelchair entrances because the regular line is not accessible.
The second week of December is typically a pretty quiet time from everything I have read (much quieter than Thanksgiving). You probably won't need a GAC. When we've been at WDW in quiet times, most of the attractions haven't had more than a 15 minute wait and many we were able to walk right on. You can always try things and go to Guest Services and request a GAC if it looks like you need one. But if the lines are short and she's pretty good about waiting, you may not find a problem at all.
Attractions providing mainstream queue access include:
Magic Kingdom® Park
Ariel's Grotto
Astro Orbiter
Buzz Lightyear's Space Ranger Spin
Donald's Boat
Judge's Tent
Mickey's Country House
Mickey's PhilharMagic
Mike Fink Keelboats (seasonal)
Minnie's Country House
Pirates of the Caribbean
Space Mountain®
Splash Mountain®
Stitch's Great Escape!
The Barnstormer at Goofy's Wiseacres Farm
"The Enchanted Tiki Room Under New Management"
The Hall of Presidents
The Magic Carpets of Aladdin
The Many Adventures of Winnie the Pooh
The Timekeeper (seasonal)
Tomorrowland® Indy Speedway
Toontown Hall of Fame
Walt Disney's Carousel of Progress (seasonal)
Epcot®
FUTURE WORLD
Imagination!: All Attractions
Innoventions East
Innoventions West
Mission: SPACE
Test Track
The Living Seas: All Attractions
The Land: All Attractions
Universe of Energy: "Ellen's Energy Adventure"
Wonders of Life: All Attractions (seasonal)
WORLD SHOWCASE
China: "Reflections of China"
France: "Impressions de France"
FriendShip Boats
Norway: Maelstrom
The American Adventure: "The American Adventure"
Disney-MGM Studios
Disney-MGM Studios Backlot Tour
Fantasmic!
Lights, Motors, Action! Extreme Stunt Show
Muppet*Vision 3D
Playhouse Disney - Live On Stage!
Rock 'n' Roller Coaster® Starring Aerosmith
Sounds Dangerous - Starring Drew Carey
Star Tours
The Great Movie Ride
The Magic of Disney Animation
"The Twilight Zone Tower of Terror"
Voyage of the Little Mermaid
Walt Disney: One Man's Dream
Who Wants To Be A Millionaire - Play It!
Disney's Animal Kingdom® Theme Park
Caravan Stage: "Flights of Wonder"
DINOSAUR
Grandmother Willow's Grove: "Pocahontas and Her forest friends"
It's Tough To Be A Bug
Kali River Rapids
Kilimanjaro Safaris
Lion King Theater: "Festival of the Lion King"
Maharajah Jungle Trek
Primeval Whirl
Theater in the Wild: "Tarzan Rocks!"
The Boneyard
TriceraTop Spin