The real question here is why Applejack never introduced herself.
Storywriter: Personally I think it would be easy enough to divide the main characters of MLPFiM up and pair them with the Crystal Gems considering similar personality traits and other character traits:
Twilight and Rarity: Pearl.
Applejack and Fluttershy(especially later seasons fluttershy (season 5 spoilers) https://www.youtube.com/watch?v=J6r5Z7W-J5k ): Garnet.
Rainbow Dash and Pinkie Pie: Amethyst.
Spike and the CMCs: Steven
Also I dont know Pearls actual fan nickname(if she has one), but thats the one Id give her.
Oh and umpretend Twilight has wings. Im not even sure if theres an Alicorn Twilight model for MMD yet.
Pearl Model: http://finnyeh.deviantart.com/art/MMD-Download-Pearl-Updated-524997061?q=gallery3AStevenUniverseMMD2F54086852&qo=10
Garnet Model: http://finnyeh.deviantart.com/art/MMD-Garnet-DOWNLOAD-523614657
Ponies are by ttasattasa on bowlroll.