Zephany Nurse, who is now 17, was seized from a Cape Town hospital in 1997.
Since then, she has been raised by the woman who allegedly abducted her, authorities say.
In a strange twist, she lived in the same city as her biological parents, who admit she's having a hard time adjusting to her new reality.
"She's broken, and we'll fix it," said her father, Morne Nurse.
The 50-year-old woman accused of kidnapping her was freed on bail Friday after the government agreed she's not a flight risk. The suspect is not allowed to contact potential witnesses, including the teen.
"We are very concerned with the well-being of the young woman," Social Services Minister Albert Fritz said. "She's taking on her last year of schooling. She's doing very well. She's a strong, assertive young woman, and it's clear she was brought up in a good home."
Fritz said his department is approaching the case with "extreme" sensitivity.
"We are concerned with the well-being of everyone involved, the young woman, her biological parents," he said, "but also can't forget about the father who believed she was his daughter."
A captivated nation
The Nurses case has stunned the nation, with throngs attending Friday's bail hearing. The courtroom in Cape Town was so crowded, her biological parents had nowhere to sit.
Nurse was allegedly kidnapped at birth and found after an improbable coincidence. She was living and going to school in Cape Town, where her biological family lives.
South African police said the woman, who was arrested last week, has been charged with kidnapping and accused of pretending to be her biological mother.
The teen crossed paths with her biological parents after they unknowingly enrolled their second daughter at the same school she attends.
Fellow students told the younger daughter that someone at the school bore a striking resemblance to her, according to the South African Press Association, an independent news agency.
The second daughter, who was born four years after the kidnapping, started eighth grade at the school this year, the news agency reported.
After other students told her a girl in her final year of school looked just like her, she befriended her, the news agency reported.
Eventually, Celeste and Morne Nurse met their younger daughter's new friend and were so taken by the similarities, they contacted authorities.
Police arrested the woman after a DNA test.
'Under the circumstances, I am doing fine'
The teen is in the custody of social services. Her parents have been allowed to visit her for short periods, the news agency reported.
She released a statement, via the Centre for Child Law, which is representing her.
"I want to say thank you to all the people who supported me through this, for continuously praying and never giving up on looking for me," she said.
"Under the circumstances, I am doing fine."
The alleged victim hasn't been identified because she is a minor. The media have given her the name Zephany to ensure her privacy.
The suspect returns to court on May 29.