Anderson said she was only free of Leaf after he was sent to prison for a second time for molesting another minor.
At the age of 14, Anderson was hired as a babysitter for the Willis family. She said the first assault occurred in the backseat of a car during a driving lesson. Anderson said Willis pulled her into the back of the car and raped her.
Anderson said the second assault occurred at her home when Ernie Willis showed up there.
"He locked the door behind him and pushed me over to the couch. I had a dress on and he pulled it off. I pushed my hands against his shoulders and said 'No,' but he didn't stop," Anderson said.
When Anderson's mother contacted Pastor Phelps, he insisted on the public apology, according to Anderson. At the same time the church congregation also heard a confession from Willis for being unfaithful to his wife. Former church members say that the confessions were presented as separate issues, but eventually some church members connected the dots.
Matt Barnhart, 41 and a father of four, says he witnessed the confession just six months after he joined the church, and it bothered him for years. But he says he felt that he could not speak out. "The whole culture is, no, you don't question the ministry, you don't question the pastor," he said.
Willis continued to be a member of the church "in good standing," according to Barnhart, and girls continued to babysit for him. After some time, Willis left the church, he said.
By January 2010, Barnhart had quit his membership after 15 years. "She's a brave girl," said he said of Anderson speaking publicly about it.
After attending college in Wisconsin, Anderson married and settled in Arizona. Anderson said she has a "wonderful husband who is 100 percent supportive." Anderson also stays in touch with her first-born's adoptive parents, whom she said provide a "very stable and good home" for her daughter.
The couple does not intend to go back to an Independent Fundamental Baptist Church.
"Going forward, we wouldn't raise our children and subject them to that," she said.
Still, Anderson says she hasn't abandoned God or her faith.
"My relationship with God is fine. I'm not mad at God," she said.
She says she knows what to tell her children about that dark chapter in her life.
"I would just say, 'Mommy went through a time where some bad people did some, some tough things ...but we've made it through,'" she said, "'and God is still good.'"
Watch the full story on "20/20" tonight at 10 p.m. ET.