JOHANNESBURG, South Africa (CNN) -- Fifteen girls at Oprah Winfrey's South African leadership academy blew open the abuse scandal that the talk show host says shook her to her very core.
Oprah Winfrey tells a Monday news conference how she found out about abuse charges and what she did.
Winfrey, on Monday, praised the teens who chose to approach the school's CEO in an environment that the millionaire described as fearful and encouraging silence.
"They represent, those 15 girls, the new generation of youth in South Africa who fearlessly take back their voices to speak up about their concern for their fellow classmates," she said, speaking to a news conference in Johannesburg by satellite hookup from Chicago.
The woman arrested in the case, Tiny Virginia Makopo, 27, was formally charged Monday with 13 counts of abusing and assaulting students at the school. She pleaded not guilty and was released on bail.
Winfrey said police in South Africa had asked her not to speak about the case publicly until an arrest was made, and she was now free to discuss the details.
Winfrey -- who has spoken publicly about the abuse she suffered as a child -- said she first heard that there was a problem from the school's CEO, John Samuel, on October 6. Watch how Winfrey heard about the abuse and what she did »
"Mr. Samuel informed me that 15 girls had come to his office to see him with a list of grievances, including suspected sexual abuse of one of their classmates by a dorm matron," she said.
School authorities removed Makopo from the campus and notified police, Winfrey said, and set up an independent team of investigators "because my experience with child predators is that no one ever, ever abuses just one child."
The remaining dorm matrons were removed because students were afraid of "repercussions," Winfrey said, and teachers were assigned to oversee the dorms. She said students cheered and cried for joy when they heard about the change.
"I told them that although they had apparently been living in an atmosphere that repressed their voices, that this was a chance for them to break the silence and to take their voices back," she said.
As the investigation developed, five other girls stepped forward to say they had been victims, and new facts emerged about the student whose case had inspired the complaints by the group of 15.
The girl had left the school earlier in the year, Winfrey said. The explanation she had been given was that the student's mother wanted to spend more time with her; but other students later said it was because of problems with a dorm matron.
"I am prepared to do whatever is necessary to make sure that the Oprah Winfrey Leadership Academy for Girls becomes the safe and nurturing and enriched setting that I had envisioned," Winfrey said. Watch Oprah talk about being a "momma bear" to the children »
"Knowing what I know now, the screening process was inadequate" for Makopo's position, Winfrey said. "We are going to redefine what that position should mean and what the qualifications for that position should be."
She said the contract of the school's headmistress will not be renewed when it expires at the end of the year.
Winfrey said the school was in the process of getting cell phones for the girls so they could call her directly and that some of the students were getting counseling.
Makopo faces charges of assault, indecent assault, and crimen injuria.
Indecent assault is defined in South Africa as touching the private parts of another person without consent; crimen injuria involves verbal abuse which violates the victim's dignity.
The state alleges there were seven victims. Six are between the ages of 13 and 14 and one was 23.
It is not clear when the abuse happened, and only some of the allegations are known. Police have confirmed that one instance involves Makopo allegedly grabbing a girl by the throat and throwing her against a wall, but Winfrey also mentioned sexual abuse of the girls.
The prosecutor said that "as a dormitory parent, she [Makopo] was in a trusted position," and that Makopo abused that trust.
Makopo was released on bail of 3,000 rand [U.S.$460]. Her next court appearance is December 13.
Winfrey said when she first heard about the abuse charges, she cried for half an hour.
"I was so stunned I couldn't even wrap my brain around it," she said. "Within the hour I pulled myself together and started making calls and preparing for what to do next and how to best look after the girls."
"What I know is, is that no one -- not the accused nor any persons -- can destroy the dream that I have held and the dream that each girl continues to hold for herself at this school," she said.
"We will show that the resilience of the human spirit is actually stronger than poverty, it's stronger than hatred, it's stronger than violence, it's stronger than trauma and loss, and it's also stronger than any abuse." E-mail to a friend
CNN Correspondent Robyn Curnow contributed to this report.
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