"You must have been the person who removed the child from hospital," High Court judge John Hlophe told the woman who claimed to have been handed the baby at a train station after entering into a private "adoption" programme.
"Your story, if anything is a fairy tale and the court rejects it with the contempt it deserves."
The 50-year-old accused, who cannot be named to protect the new identity of the kidnapped girl, remained grim-faced staring at the judge.
The accused was denied bail and ordered to return to court for sentencing on May 30.
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The girl's real identity came to light in February last year, when her younger biological sister began attending high school and pupils pointed out her remarkable likeness to a final-year student.
The younger girl told her parents, who met the older girl and immediately believed she was their long-lost baby.
They called the police, and DNA tests confirmed that the girl was indeed their child, whom they had named Zephany Joy Nurse.