A powerful and revealing book detailing life in the repressive Gloriavale commune has been released by the granddaughter of founder Neville "Hopeful Christian" Cooper.

Lilia Tarawa has written Daughter of Gloriavale - My life in a Religious Cult about the community at Haupiri near Greymouth on the West Coast.

Founded in 1969, Gloriavale reportedly has around 500 members with families living according to a strict interpretation of Christianity and working unpaid in community farming and aviation businesses.

Tarawa, who with her parents Perry and Miracle Tarawa fled Gloriavale eight years ago, now lives in Christchurch.

In her book the 26-year-old writes of her 18 years in the commune, her relationship with her maternal grandfather "Grandad Hopeful", and the day her family eventually fled the Christian community.

Tarawa reveals the level of power her charismatic and controlling grandfather had over the community. Even when Cooper was found guilty of three charges of sexual assault in 1995 and served a jail sentence he was held in high regard and gave religious instruction from his prison cell.

One of 10 children, Tarawa said she was "brainwashed" but at the same time constantly struggled with the restrictions placed on her.

Women were expected to serve and "submit to men" and anything else was seen as "ungodly", she said.

In the book Tarawa claims arranged marriages were decided by Cooper who also believed girls were ready for marriage, and sex, as soon as they began their menstrual cycle.

It was only the New Zealand law that stopped marriages before the age of 16.

Her grandfather, Tarawa said, "would have happily married off children of 10 or 12 years" of age if the law had permitted it.

Despite the oppressive environment, Tarawa also writes fondly of the relationships forged and the life skills acquired at Gloriavale.

And when she and her family emerged from the community she tells of learning how to apply makeup via YouTube tutorials, buying her first pair of jeans at 18 and not knowing how to pay with an eftpos card.

Now a life coach with her own business, Tarawa credits her upbringing and the strength of her parents to leave Gloriavale, with her success.

Two of the older Tarawa children had already fled Gloriavale years earlier and when a third child left, Perry and Miracle Tarawa decided they had to leave too.

"I lost a lot of the people I loved when we fled the religious community I'd been raised in. I wrote a book about it. Coming to terms with that loss is a journey I'm still on."