Christina Grant's family, who live in New South Wales, flew her to Australia following the death of her son and carer, Robert, in February 2015.
Her family believed they had met the requirements of her visa, which expires later this month.
Immigration officials said they had been working with the family and made no arrangements to remove Mrs Grant.
However, the grandmother's family told BBC Radio's Good Morning Scotland programme that they had not found Australia's immigration department helpful and had gone to specialists for assistance.
They could apply for a new visa but were told that this could take 30 years to resolve.
The Grant family had hoped that because of her age and state of her heath that her situation might be treated a special case.
Mrs Grant's surviving son Allan and his wife Diane believe they have done everything to meet the rules of her visa after she moved to live with them in Australia.
Mrs Grant is booked on a flight back to the UK on 26 July, the date her visitor visa expires.
Her family told BBC Radio's Good Morning Scotland programme that the alternatives were the possibility of deportation or "years of limbo" while trying to obtain a new visa.
Mrs Grant, who is partially sighted and has dementia, was living near Grantown on Spey in the Highlands.
Her son Robert had been helping to look after her.
Because of the state of her health, Allan and Diane asked her to move to Australia and live with them.
They applied for a visa for her to come to Australia.
A condition of her visa was that she had to depart Australia once every 12 months but could return.
Concerned that Mrs Grant was not fit enough to fly out of Australia to meet this requirement, her family booked her on a cruise to Vanuatu, a group of islands in the South Pacific Ocean.
They believed that this trip would meet the visa requirements.
However, after the cruise the Grants were told by the Department of Immigration and Border Protection that the visa rules had not been met.
Diane told Good Morning Scotland that immigration specialists had told the family that applying for a new visa could take up to 30 years to come through.
They are now preparing to fly with Mrs Grant back to Scotland.
Diane said: "We will have to help her find a home over there.
"We have our own life here in Australia and, while I don't want to live there, Mum wants to live here."
The Grants have highlighted their case in an effort to alert other families that may find themselves in the same situation.
The Department of Immigration and Border Protection said all visitors to Australia must hold a valid visa for the duration of their stay and comply with the conditions of that visa.
A spokesperson said: "The department is familiar with Ms Grant's case and is not making any arrangements to remove her from Australia.
"The tourist stream visitor visa is normally valid for stays of up to 12 months and, as with all visitor visas, is designed to facilitate temporary visits to Australia rather than long-term stays or residence.
"Conscious of her circumstances, the department has been working with Ms Grant to resolve her visa status, since her visitor visa expired.
"Ms Grant has no current visa applications with the department."
A 96-year-old woman is preparing to return to Scotland from Australia after a visa wrangle.