A FORMER mayor has bequeathed her three daughters "30 pieces of silver" - or $1.50 - each from her $3.5 million estate because she believed they conspired over the death of her mother.

Valmai Roche left the same amount to her ex-husband, John Roche, a former property developer who was Adelaide City Council Lord Mayor from 1975-77.

Two of Ms Roche's daughters say their mother was "delusional" and they are challenging her will in the South Australian Supreme Court, The Advertiser reports.

Before her death, Ms Roche's mother, Dorothy Maud Haber, was being cared for in a nursing home. The documents do not say how or when she died.

Ms Roche, who died last year aged 81, left "30 pieces of silver of the lowest denomination of currency" - or 30 five cent pieces - claiming it was "blood money due to Judas" to each of her daughters.

The daughters - Deborah Hamilton, Fiona Roche and Shauna Roche - were also left equal shares in their mother's jewellery, on condition they read and correctly answered questions relating to her personal diaries from January, 1974, until the date of her will, which was signed in October 1981.

The will left the remainder of her estate to the Knights of the Southern Cross - a Catholic charity for men.

Ms Roche also "specifically excludes" her children and former husband "from any further benefits" because her daughters "have been adequately provided for . . . and because of their estrangement" during her later years.

Mr Roche was excluded from further benefit due to the "irretrievable breakdown" of the couple's marriage, which ended in divorce about November 1983.

Ms Roche made only one addition to her will. In 1987, she left a French Empire style desk to daughter Fiona.

Fiona Roche now heads the family's Roche Group of companies - a family empire that regularly appears in the BRW Rich 200 list.

Documents before the court do not provide a formal valuation of Ms Roche's estate, but it is estimated at $3.5 million.

Ms Hamilton alleges her mother held "fixed, false and incorrigible views".

Ms Hamilton alleges her mother's "delusions" rendered her incapable of "making a reasonable and proper disposition of her estate", making her will invalid.

The matter returns to court next month.