AUSTRALIAN mining magnate Gina Rinehart is on course to become the world's richest woman, Forbes magazine reported, as details emerged of a legal tussle with her children over part of her fortune.

Forbes Asia said the 57-year-old was the wealthiest woman in the Asia-Pacific region and the richest Australian, with a fortune estimated at US$18 billion (S$22 billion) and set to rise as she expands her iron ore and coal projects.

"If commodity prices hold up, Rinehart could challenge Christie Walton, who is said to be worth US$24.5 billion as the world's richest woman," Forbes said.

The latest assessment came as Ms Rinehart's daughter said she was down to her last A$60,000 (S$80,000) and needed a bodyguard, in an e-mail revealed by a court handling a legal battle within the family.

The messages released by the New South Wales Supreme Court on Thursday showed that Ms Hope Welker told her mother she needed a cook and a housekeeper, as well as security staff because of the family's highly publicised wealth.

The US-based Ms Welker, 27, added that she also needed a safer apartment, but could not afford it.

"I don't think you understand what it means now that the whole world thinks that you're going to be wealthier than Bill Gates - it means we all need bodyguards and very safe homes," Ms Welker wrote in July last year.

"I don't have the money to protect myself or my children and it scares me. I should have enough money to have a bodyguard, housekeeper and cook. "

The personal e-mail came to light as three of Ms Rinehart's four children challenge their mother in court over control of a family trust reportedly worth in excess of A$3 billion, AFP reported.

Mrs Rinehart, who recently bought into the media sector, has sought to have details of the case suppressed, but Justice Michael Ball allowed the e-mail to be released.

An e-mail from another daughter, Bianca, highlighted the children's concerns as they struggle to deal with speculation regarding their mother's wealth.

The daughter referred to a fake collar-bomb placed on a Sydney schoolgirl last year.

"Chum, no doubt you heard about the unnerving situation yesterday involving a bomb and an 18-year-old girl," Ms Bianca Rinehart wrote to her mother after the incident.

"Although we were not targeted this time, we are, by all accounts, the highest-risk family in all of Australia for future similar attacks."

This article was first published in The New Paper.