She was present during her father's psychotic break that led him to kill his own family after creating his clown-themed outfit. She was at the madman's mercy until she managed to grab a pair of large scissors and stab her father in the eye, giving her a chance to escape.
She is apparently the only person to ever escape Sweet Tooth after he decided to kill them, causing the killer to dub her "the one that got away". He is obsessed with finding and killing her, to the point where he joins the Twisted Metal competition solely to wish for Calypso to send him to her hiding place.
Sophie's Fate (SPOILERS!)
After escaping from her insane father, Sophie ended up in a hospital, where doctors tried to help her. Unfortunately, her mind was shattered by the events she suffered, causing her to commit suicide by shooting herself in the head. Some years later, Sweet Tooth attacked the same hospital in search of her; despite killing almost everyone in the building, he failed to learn the truth.
When Sweet Tooth made his wish to find Sophie, Calypso sent him to her by teleporting him into her long-buried coffin. By now, Sophie had become a blackened skeleton, infuriating her father as Calypso explained what had happened to her. In the end, Sweet Tooth ended up sharing his daughter's grave, which Calypso mocked by spray painting his name over Sophie's tombstone.
Later, Sophie's grave would be disturbed by her brother, Charlie, who had also survived their father's attack. He had come to believe that he was the heir of Sweet Tooth's work, leading him to dig up his sister's coffin to retrieve the iconic clown mask before setting off in his father's former vehicle.
Some time after Charlie left, Calypso returned to the grave, musing that Sophie had much anger and potential for causing pain within her. Deciding to put those feelings to use, Calypso used his powers to revive Sophie as a loyal follower with an outfit similar to Sweet Tooth's own, complete with mask and flaming scalp. The exact reasons of her resurrection are unknown, but it seems that Calypso intends to use her as a loyal enforcer of his will, or possibly as defence against the vengeful Charlie.