Mia is the youngest two children in the Toretto family. Her father was a professional stock driver who owned a 1970 Dodge Charger R/T. Her older brother, Dominic, helped their father build the Dodge Charger. Additionally, the Toretto's owned and ran a market and cafe shop.
Mia grew up in the company of Dominic's friend, Vince, who they knew since Dominic was in second grade; and Letty Ortiz, a girl from their neighborhood who befriended when she was ten years old. When she was sixteen, Letty and Mia's brother became romantically interested in each other.
Mia was presumably did not attend the stock car race where her father was killed in an accident caused by Kenny Linder, a fellow stock car driver, but was devastated all the same. When Dominic attacked Linder, he was arrested and sent to Lompoc Prison for assault. At some point before or after, they befriended the likes of illegal street racers and mechanics, Leon and Jesse.
Mia was aware of her brother's illegal and criminal activities, stealing from trucks transporting electronics and other goods, and participating in street races as an act of keeping his passion for racing alive after he was permanently banned from the tracks for attacking Linder. Mia presumably was taught how to drive by her father or brother. She ended up becoming rather close to undercover federal agent Brian O'Connor.