A registered sex offender, he served time in jail for a crime against another girl. When she later confided with church members they allegedly told her not to report the case.
At the age of 14, Anderson was hired as a babysitter for the Willis family. She says the first assault occurred at her home when her parents were away.
"He said he wanted to talk to me about something so I let him in the house," she told police. "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."
A year later, Willis allegedly assaulted her during a driving lesson behind a local business when he asked Anderson to "switch seats," according to her statement. He pulled her into the back and "raped" her, she said.
When her mother contacted 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.
At the time, Phelps said Willis was "99 percent to blame" and Anderson held "1 percent" of the responsibility.
Phelps insisted they were separate cases as each confessed at separate sides of the auditorium, 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.
"Pastor Phelps was a statesman, an excellent speaker," said Barnhart. "I was always impressed by him and thought the world of him. But all that changed after that. I lost respect for him."
Willis lost the deaconship, but 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.
Just last year, Barnhart quit his membership after 15 years when his family was in "fierce need" of counseling.
"How can we go to a pastoral staff when we think they might have let the rapist of a 14-year-old go?" he told ABCNews.com. "How can they hurt these kids and call themselves a real place that teaches the gospel?"
"She's a brave girl," said he said of Anderson speaking publicly about it.
After having her baby in Colorado, Anderson attended Olson's college in Wisconsin and is now married with three additional children. She stays in touch with her first-born's adoptive parents, whom she said provide a "very stable and good home" for her daughter.
Anderson said she has a "wonderful husband who is 100 percent supportive." He works at a nearby university.
The couple does not intend to go back to the Independent Fundamental Church (IFB). "Going forward, we wouldn't raise our children and subject them to that," she said.
She hopes one day to help others who have been similarly traumatized by sexual abuse. Anderson says she would tell them: "Truly, it's really important to know that it's not your fault," she said. "You need to tell someone, and talk until someone will listen."