"I have to make that decision by the end of this year," she said regarding whether she would continue the show. "I am literally in thoughtful prayer and consideration to continue to go ahead. You'll be hearing about it before the end of the year."
"I will tell you that in my preparation for my interview, I watched the interview you had done seven years ago," Winfrey told "Good Morning America" co-anchor Diane Sawyer, who interviewed Houston in 2002. "Because I watched that interview I got up the next morning and prayed. What I realized is … she was not ready to talk. She was not forthcoming, she was still in denial."
Winfrey and Houston had a private conversation before their interview, and Winfrey said that Houston is now "quite a different person."
"She said she wanted to tell her story," Winfrey said. "She wanted to tell the truth."
"She gave it up," Winfrey said of the exclusive interview that will air in two parts Sept. 14 and 15. "She talked about difficulty in her marriage [to Bobby Brown], how that started. She talked about the drugs, she talked about what drugs she was doing. ...There wasn't a question I asked that she didn't answer."
During the interview, Houston spoke about a time when her mother came to her home with the police to conduct an intervention and get Houston out of the house and off drugs.
"Now looking at it, I see the love and passion that my mother had for me," she told Winfrey. "She came and said, 'It's not worth it.' She said, "If you move, Bobby, they're gonna take you down. Don't you make one move.' And he stood there like, he was scared. And she said, 'Let's go.' She said, 'Let's do this.' She said, 'I'm not losing you to the world. I'm not losing you to Satan. I'm not doing this. I want my daughter. I want you back. I want to see that glow in your eyes. That light in your eye.'"
Winfrey said, "I think it's because of her strong faith in God and the support of her family that she made it through."
Houston's new album "I Look to You" -- her first in seven years -- hit stores Aug. 31, and she kicked off her comeback with a performance on "GMA."
Houston, 44, said on "GMA" that she got through the difficult period in her life with the support of family, friends, fans and faith.
"Don't be worried anymore," she said. "If you know God don't be worried."
This week, "The Oprah Winfrey Show" shut down Chicago's Michigan Avenue for a block party featuring an appearance by the Black Eyed Peas that airs today. Friday's show will feature ESPN's Erin Andrews talking for the first and only time about the video showing her naked in a hotel room that surfaced on the Internet in July.
"I opened up the computer and could feel my heart pounding," Andrews told Winfrey, describing the first time she saw the video.
"Imagine yourself getting dressed this morning and having a camera in your bathroom or the bedroom and have all that out on the Internet today," Winfrey, who didn't view the video, said on "GMA."