But Wampler did not always have her family's support, something she said is common in incest cases.
"Unfortunately, there is so much denial," Wampler said. "There were family members who wanted to sweep it under the rug, and there are some I don't talk to because they are in such denial."
Two of John Phillips' former wives said Mackenzie Phillips is lying.
Michelle Phillips, Mackenzie's stepmother and a member of the Mamas and the Papas, told the Hollywood Reporter she believes the allegations are false.
Michelle Phillips said Mackenzie had "a lot of mental illness" and that "she's had a needle stuck up her arm for 35 years."
"Mackenzie is jealous of her siblings, who have accomplished a lot and did not become drug addicts," said Michelle Phillips.
But Chynna Phillips, Mackenzie's stepsister, told US Weekly that she believes the story.
"Somebody could have dropped a piano on my head, and I probably wouldn't have felt it," Chynna Phillips said of the time Mackenzie first told her. "But I knew it was true. I mean, who in their right mind would make such a claim if it wasn't true?"
Mackenzie Phillips told Oprah that one of the reasons she wrote the book was to earn the right to speak about forgiveness.
"Forgiveness isn't for the other person. It's not to give the other person peace," Phillips said. "Forgiveness is for you."