JOHANNESBURG, South Africa (AP) _ Oprah Winfrey said Monday she wept after hearing allegations that a dorm matron at her academy for disadvantaged girls had abused students. She accused school officials of telling the girls to “put on happy faces” when she visited.

Though she said she was not responsible for hiring at the school, Winfrey said the screening process was inadequate and “the buck always stops with me.” She said the head mistress’ contract would not be renewed and promised a shake-up, indicating school officials had tried to keep the facts of the case from her.

“When I first heard about it I spent about a half-hour going around my house crying,” Winfrey said at a news conference by satellite hook-up. She said learning about the allegations was “one of most devastating experiences of my life.”

Tiny Virginia Makopo, 27, faces 13 charges of indecent assault, assault and criminal injury committed against at least six students aged 13-15 and a 23-year-old at the school. Makopo, who said she was innocent, was freed on bail Monday.

Winfrey said she was initially told a girl who accused the matron of abuse had left the school because the girl’s mother wanted to spend more time with her. She said girls at the school, which she visited frequently, told her they were instructed “to put on happy faces” when she was there and not complain.

Winfrey, who has in the past spoken of the abuse she suffered as a child and campaigned for laws in the United States to protect children from abusers, said that because of the high rates of rape and sexual abuse in South Africa, she had worked to ensure outsiders would not be able to reach students at the school.

But “as often is the case, child abuse, sexual abuse happens right within the family, right within the confines of people you know,” she said.

Winfrey has spoken in the past of being raped by a distant cousin at age 9 and then abused by three other men, trusted family friends.

Winfrey said the school’s chief executive John Samuel told her in early October that a group of 15 girls had come forward with a list of complaints including the sexual assault of one of their classmates.

She then called for an independent investigation to determine the extent of the allegations. The investigation was headed by Richard Farley, a Chicago detective who works with child abuse cases.

“My experience with child predators is that no one ever abuses just one child,” she said.

Winfrey said she flew to South Africa to speak with the pupils and encourage them to come forward with their complaints: “It was a chance to break the silence.”

The school announced Oct. 17 that a dormitory matron had been suspended amid allegations of serious misconduct. The Oprah Winfrey Leadership Academy for Girls said private U.S. and South African detectives were investigating, as well as South African police.

On Oct. 20, Winfrey said Monday, she flew to South Africa again to meet with parents: “I apologized for the unfortunate circumstance and promised changes.”

Winfrey opened the academy outside Johannesburg on Jan. 2, with celebrities such as Tina Turner and Spike Lee in attendance, as well as former President Nelson Mandela.

The lavish $40 million school was the fulfillment of a promise she made to Mandela six years ago and aims to give 152 girls from deprived backgrounds a quality education in a country where schools are struggling to overcome the legacy of apartheid.

Winfrey was adamant that the scandal had not dented her desire to help the girls in her school.

“No one – not the accused or anyone else – can destroy the dream I have held or that the girls hold. Their light will not be diminished by this,” she said.

Samuel, the school’s superintendent, told reporters Monday there was now a sense of relief at the school and that life was beginning to return to normal.

“We are beginning to heal. The spirit of the girls remains strong,” he said.