Sometimes, you don't get a back story.
Things are how things are because that's the programming and you stick to it. The stands are set up that way because it is, the track curves where it does because the programmers liked it, and the candy trees double-stripe their branches because someone outside their game had a sick sense of humor and nothing better to do. The police never were elected to their positions, they were made that way.
There is many an occasion that Taffyta will take a look in her side mirror and wonder what things would have been like if she had been made different. What if she had longer hair, or a different name? What if they changed her color palate? But those weren't questions you asked, they ranked up there with 'Why does Nougetsia look like a blue version of Minty Zaki' and 'Rancis, why do you sleep with a mirror every night'. They weren't important. They didn't pertain to the main point of the game.
She envied other games, truly. Even the characters with a back story that was tragic to the point of sheer stupidity, or with just minor details that made them who they were. She was a jerk because she was programmed to be, right? Or was she that way because she wanted to be? Her motto was 'Stay Sweet', shouldn't she live by that? She would claim that it kept her up at night, but since her programming didn't require her to sleep that was sort of a moot point.
Every time she wanted to say 'when things first started' she caught herself. When things first started, Vanellope was a princess in a pink dress with a pink castle. That didn't last very long- maybe a week? A month? Things got blurry in her head, it did for everyone. They all were glitches now, just in a different way. The source code had gone sourer than Sour Bill, and the time before just seemed to blur. She always meant the time when King Candy was around, the way things had been for years. Vanellope may be princess- or president, whatever- but King Candy had that position for a bit longer, and she was still getting used to things.
There were a lot of changes she had trouble adjusting to for a long time, and one of those changes was her sudden lack of importance. King Candy may have been better than her, but that didn't make him a total jerk. And even after realizing that ninety percent of what he said was more malarkey than 'The Swizz', she still held on to things she hoped were at least a little true. Little things, like 'you're my favorite' and 'I'd be lost without you, Taffyta'.
There were times she'd drive her car somewhere and sit in silence, usually in the junkyard or over by the chocolate river. She wanted time alone. The others respected that. (Well, either that or they didn't care about her anymore; she didn't really feel the burning need to ask. 'Stay Sweet' her sucker, they cozied up to Vanellope like cavities.) She had to sort through everything. All her memories. All the lies.
So. Many. Lies.