So it was shock for Raymond Pearson to learn his 82-year-old sister had left everything to a stranger when she eventually died in 2008 after suffering from dementia.

Police will allege Ms Pearson was targeted by a family gang, who allegedly prey on elderly victims with cognitive impairments in order to become the beneficiaries of their multi-million dollar estates.

Almost seven years after Ms Pearson's death, Auburn police detectives arrested a mother-of-four who allegedly posed as a cleaner and befriended Ms Pearson in her Canterbury home sometime after she was diagnosed with dementia in 2003.

Victoria Adams, 44, was arrested at her two-storey Blair Athol home in western Sydney on Friday and charged with conspiring with others to cheat and defraud the $1.7 million estate of Ms Pearson.

She was granted conditional bail and expected to appear before Burwood Local Court next month.

Police allege Ms Adams, conspired with her father Alex Johan, a convicted criminal, and other family friends to be publicly seen with Ms Pearson in the years before she died.

Alex Johan died on Australia Day this year – days before police were to arrest him for his role in masterminding the plan to defraud Ms Pearson of her estate.

Officers have also arrested a number of Ms Adams' relatives for their roles in allegedly tricking a 97-year-old man into signing over his  $3.4 million estate and allegedly stealing more than $500,000 from a 87-year-old man who suffered from a mental illness.

Police allege Ms Adams befriended Ms Pearson sometime after 2003, conspired to obtain her signature and made a fraudulent will without the victim's knowledge.

The will was fraudulently backdated to 1999 and witnessed by an associate of Ms Adams, police allege.

A paper and fibre analyst said the piece of white paper used had not been manufactured until at least 2006 – seven years after the will was dated.

"Investigators will allege that the accused played an active and significant role in the conspiracy to defraud the savings from the estate of Edna Pearson," according to the police fact sheet.

"Although it is not disputed that the accused became involved in the life of Edna, investigators believe that the history of the relationship between the accused and Edna was fabricated by the conspirators."

Ms Pearson's niece Suzanne Corney said her family had been "ripped apart" by the deception and spent years thinking Ms Pearson had died hating her relatives.

"We thought she had dementia and we didn't think twice about her being funny with us – we thought it was her illness," she said. "Edna didn't want to talk to anyone – she stopped talking to her brother, who lived next door to her."

Mr Pearson entered a settlement with the accused, Ms Adams, so that he could remain in the adjoining property to Ms Pearson in Robert Street, Canterbury.

But about a year after the settlement, detectives stumbled across evidence relating to Ms Pearson's estate during an investigation into the will of Herbert  Luscombe, 97, who signed over his estate to one of Ms Adams' relatives in 2006.

Mr Luscombe was  suffering from heart disease and had only days earlier had a hip replacement when police were told he signed his $3.4 million estate to a mystery blonde woman.

Mr Luscombe's will was witnessed by the same associate of Ms Adams, who witnessed the fraudulent will of Edna Pearson.

Police are appealing for anyone with information to contact Crime Stoppers on 1800 333 000.