Marli van Breda has indicated to the State that she would not want to be made available to the defence, the Weatern Cape High Court heard on Monday.
Prosecutor Susan Galloway told Judge Desai that the teenager, who along with her triple murder accused brother Henri Van Breda were the only survivors of the 2015 De Zalze axe attacks, had made this request.
Marli was on the State's witness list, but was not called as she had not regained her memory.
She was 16 at the time of the attack and sustained severe head wounds and a severed jugular. After being hospitalised for six weeks, she was treated at a rehabilitation centre.
She has retrograde amnesia and cannot recall anything about the attack.
She and Henri saw each other again six months after the murders.
Following his arrest, in last June, her legal representative and curator Louise Buikman said the news had been "very distressing" to Marli.
The Western Cape High Court ruled that although she is legally an adult, Buikman would continue to oversee matters concerning her.
She had not been seen at court since the start of Henri's trial.
Van Breda, 22, pleaded not guilty to axing his parents and brother to death, seriously injuring Marli and defeating the ends of justice.
He alleged that an intruder wearing a balaclava, gloves and dark clothes was behind the attack, and that he had heard other voices of people speaking Afrikaans in their home in the De Zalze Estate in Stellenbosch in January 2015.
Van Breda claimed that, after a fight with the axe-wielding intruder who was also armed with a knife, the man had escaped.
Proceedings resume on Thursday.