(CNN) -- The reaction to Mackenzie Phillips' detailed account of her sexual relationship with her father, John Phillips, has been explosive, and some of the strongest statements have come from her family.
Chynna Phillips said she doesn't think anyone could make up having a consensual incestuous relationship.
But as the former actress and musician talked with Oprah Winfrey for the second time this week -- this time about the firestorm that erupted from her hour-long interview Wednesday -- she said she doesn't regret writing her memoir, "High on Arrival."
"I understand this is a difficult thing for my family," Phillips told Winfrey via satellite Friday, "but nobody's talking about this, and if I've started a national dialogue, then I'm forever grateful."
Phillips said she has gotten letters and Facebook messages from incest survivors, thanking her for coming forward.
"It's been heartening and heartbreaking at the same time," she said.
John Phillips died in 2001.
Two of his former wives, however, have vehemently denied Mackenzie Phillips' accusations.
In an statement to CNN, Michelle Phillips, an original Mamas & Papas bandmate who divorced John in 1970, called the situation "very hurtful."
"Mackenzie's drug addiction for 35 years has been the result of many unpleasant experiences," Michelle Phillips said. "Whether her relationship with her father is delusional or not, it is an unfortunate circumstance and very hurtful for our entire family."
She spoke more strongly to The Hollywood Reporter's Roger Friedman, telling him, "Mackenzie has a lot of mental illness. She's had a needle stuck up her arm for 35 years. ... She did 'Celebrity Rehab,' and now she writes a book. The whole thing is timed."
Genevieve Waite, who married John Phillips in 1972, told Winfrey in a statement that "John was a good man who had a lot of problems, [but] he was incapable, no matter how drunk or drugged he was, to have sexual relations with his own child."
The fallout from Phillips' decision to reveal her family's secrets has been heartbreaking for her sister Bijou as well.
Bijou Phillips supplied a statement to Winfrey stating that Mackenzie told her about the incestuous relationship with their father when Bijou was 13 but later denied it.
"This news was confusing and also scary, because I'd lived alone with him since I was 3," she said. "[John Phillips] was Mr. Mom, loving and encouraging; the man who raised me would never be capable of such things."
She also questioned why Mackenzie would leave her alone with their father if he'd molested the elder sister.
Still, Bijou Phillips showed signs of measured support.
"I understand Mackenzie's need to come clean, but it hurts because the man in question isn't here to defend himself," she said. "I hope she can come to terms with this and find peace."
Mackenzie Phillips told Winfrey that her family's disbelief and anger saddened her, especially since she and Bijou Phillips have been very close. Phillips recalled the way Bijou immediately came to her aid when she was arrested last year for cocaine and heroin possession.
"I love my baby sister, and I miss having contact with her," Mackenzie said.
"By the time Bijou was living with my father, I felt she was safe. I did take her out of there if I felt like she wasn't being watched properly," she said in her defense.
But she added that Michelle Phillips' statements weren't as surprising.
"When Michelle found out I was writing this book, she vowed to do everything to discredit me," Mackenzie told Winfrey. "She's having a textbook reaction, trying to sweep it under the rug. It seems so unkind and ungenerous to lash out in this way; I don't have a history of mental illness. I have a history of drug addiction."
Chynna Phillips, who also sat down with Winfrey on Friday, said she believes that her mother, Michelle, made those statements out of anger and that she does still love Mackenzie, even if she doesn't admit it.
"I think the most devastating thing is when people are in denial and don't want things on a public platform, it's not something everyone wants to share with the world," Chynna Phillips said. "It's not something my mom wants plastered all over the papers."
Chynna told Winfrey that she'd known about her sister's history with her father for about 12 years and believes that no one would go out of their way to admit having a consensual incestuous relationship.
She's also not the only one who thinks Mackenzie is telling the truth.
Jessica Woods, the daughter of former Mamas & Papas band member Denny Doherty, also wrote in to Winfrey and said her father knew about everything.
"I just watched your show," Woods wrote, "and everything she said is true. My dad told me the awful truth, and he was horrified at what John had done."
Chynna, who grew up with her mother, said that although she didn't spend a lot of time with John Phillips, the memories she had of him were positive, in spite of the heavy drug use she witnessed.
"He was a very charismatic man," she said. "He was a very talented man and a very loving man in many ways."
Now one half of the Christian music duo Chynna and Vaughan, Chynna said that her relationship with Mackenzie has grown over the past six months and that she's proud of her half-sister for having the courage to talk about her past.
"The thing is, who among us haven't done something that we're highly ashamed of in our lives?" she said to Winfrey. "Who are we to cast the first stone? In my faith, as a Christian, God told me I need to forgive. Am I happy that she put me in this position? No, I'm not. But I have to forgive. It's 13 years later, and I still haven't digested this information."
Chynna added that she hopes her sister will take her experiences and use them to help others, offering one piece of advice: "Get the Lord on board, because you'll need it."