Born to two Irish Immigrants to the united states, Vi doesn't remember her parents much at all, beyond some snatches of song and voices, and someone teaching her to braid her hair. When she was four a fire took her parents, and she and her twin sister were placed in foster care. They didn't stick there long, lasting two years before they were on the streets. It wasn't long before they fell in with bad people, who saw the use of two pretty girls for getting things past cops. Vi's life of crime started early, after all.
The Cartel that took Vi and her twin in were harsh but gentle, at least at first, with the two girls, and they both did what they could to help, but a split soon formed between them. Ami was harder, scarier and more willing to rough others up to get what she wanted. Vi was softer, sneakier and generally unwilling to hurt people unless necessary. Killing a kid was distasteful, and so Vi did what she could to make up for her short comings. She was instinctually good with computers and leaned into that, as much as she could. Life wasn't always easy, but she wasn't alone, after all, she had Ami, didn't she?
As things go, it didn't end well. At 18, Ami decided that she wanted to join the cartel, and blood in. She chose her target. Why, Vi hasn't been able to decipher, though she assumes it's because "only I can kill my twin". Either way, Vi almost lost an eye, before she was saved in the nick of time. Who it was and why she came to Los Santos is her own personal story to tell, however.