Marcel Steyn, who was 14 when the "Krugersdorp killers" went on their deadly spree, was made to believe her father never wanted her, and then turned to drugs.
Probation officer and psychologist Rosiland Macnab, who evaluated Steyn, told the South Gauteng high court in Johannesburg on Tuesday that she believed Steyn had a minor role in the gruesome crimes committed by the group.
Macnab was testifying in mitigation of sentence proceedings for the killers - housewife Cecilia Steyn, insurance broker Zak Valentine and the then-schoolgirl Marcel Steyn.
Marcel's mother and brother, school teacher Marinda Steyn who testified that killing was an adrenaline rush, and self-confessed strangler Le Roux Steyn are currently serving lengthy jail terms for the 11 murders committed by the group.
Marcel was born in Pretoria and lived with her parents, Andre Hugo and Marinda, until the age of four.
Her parents divorced and she saw her father every second weekend. Marinda told Marcel that her father did not believe she was his child. Marcel, however, who had vague memories of her father, said she felt safe with him.