It was back in the early 90's. She had just done a show that was common back then where they surprised a woman with the fact that her husband and best friend had an affair. It was obvious that the woman was in shock when she heard the news and she was basically so torn up that she was unable to function.
Oprah looked at the woman and she apologized. She told her she would pay for therapy. Most importantly she told her that she would never do one of those kinds of shows again. To the best of my knowledge, she didn't.
That was the beginning of a change in theme of her show. She went from doing the rip somebody apart for ratings thing to actually helping people. It has brought her even more success than anyone could have imagined.
It will be interesting to see if she goes on to rule the world. She has the potential.