Haynes coped by developing many different personalities.
Psychiatrist Dr George Blair-West explains that multiple personality disorder can be a sophisticated tactic developed by children who experience significant trauma prior to the age of eight.
"And the thing that seems to push the mind to do this more than anything else is realising you have no way out, that nobody is going to come and get you, nobody's there to save you, you're on your own, and you have to come up with a solution that is entirely of your own," he said.
"There is nothing wrong with Jeni's human mind or any other person who suffers from dissociative identity disorder. Their mind is just coming up with an incredibly sophisticated, clever solution to a scenario that most of us could not begin to understand or relate to."
Haynes, who grew up in Greenacre in Sydney's western suburbs, has fought for years to bring her father before the courts.
She spent 18 years at university, graduating with a degree in psychology, masters in legal studies and criminal justice as well as a PhD focusing on victims of crime.
Sydney Detective-Sergeant Paul Stamoulis agreed to take on her case nine years ago, but the difficulty was proving it happened.
Haynes had the physical injuries from the repeated rapes, but it was also decided that she would need to take the stand. She told her story of torture and abuse through the voices of her multiple personalities.
"She has a memory unlike yours or my memory," Dr Blair-West said. "Her alters are living in different time-space realities, effectively. Particularly those younger ones."
Haynes is able to bring up the alter who was present at the time certain things happened and they are able to describe the events "like it was yesterday".
"It's almost like being able to, yeah, click on a folder in a computer, open it up and read it, without any decay over a 40-year period," Dr Blair-West said.
Footage aired on 60 Minutes shows Jeni Haynes speaking with the voice of some of her different alters, which can include a four-year-old girl named "Symphony", a 11-year-old boy "Judas" and a rugged and strong teenage boy "Muscles".
Dr Blair-West has been treating Jeni for over 20 years and said if a functional EEG was being done on Haynes "you'd see different brainwaves" when she changes between personalities as well as differences in her voice.
In an attempt to protect Haynes from the trauma, the alters even helped manage her senses so she couldn't experience things like smell.
"My dad smells like burning bakelite, and the most unwashed construction worker you will ever meet. He is vile," Haynes said.
On February 21, Haynes appeared before the NSW District Court to face her 74-year-old father. Authorities had to extradite him from the United Kingdom before charging him with multiple counts of rape, buggery and indecent assault.
After being faced with the testimony of Haynes's many different personalities, her father crumbled and pleaded guilty within hours of her taking the stand.
Although Haynes is able to remain anonymous, she has chosen not to because this would also have protected her father's identity.
"I want him to walk into prison with everybody knowing what he did," she said.
Next week Haynes's father will be sentenced and she is finally looking forward to leaving the past behind.
"I want to travel. I want to make memories. They can't wipe away the past but it's time for good stuff, time to enjoy and if I don't enjoy it I'm not going to do it," Haynes said.
If you're in danger now:
• Phone the police on 111 or ask neighbours or friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay.
Where to go for help or more information:
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Pet Refuge petrefuge.org.nz
• Shine, free national helpline 9am- 11pm every day - 0508 744 633 www.2shine.org.nz
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
