Winfrey, 53, dressed in traditional African garb for the occasion, publicly praised the student and wept with emotion.
Previously, the girl had been shunned after going public in September with her claims of abuse by staff at the school, which opened in January. Winfrey subsequently apologized publicly over the claims. (In the scandal's aftermath, an investigation was launched, and a dorm matron was relieved of her duties and arrested.)
Winfrey also paid a secret visit to the school – and to the girl and her father – earlier this week.
An 'Excellent' CelebrationThe father, whose name is being kept private, described Tuesday's celebration as "excellent." Prepared by Oprah's private chef, the dinner included turkey and salad.
"I am still tasting that food," he tells PEOPLE. "I have never had anything like it before. Everything was top of the range."
He is also optimistic about the future of Winfrey's academy. "After finally meeting Oprah all our stress went away. There was evil in that school and we defeated the Devil," he says.
"I'm urging all the parents to work with Oprah in order for the school to be a success. We must all move on from what happened in the past."
He adds: "Our daughters will get the best education and will not be exposed the temptation of boys, drugs and HIV. I believe the hands of Oprah are now open. She will listen to our problems."