Marie, not her real name, discovered in June a government department had granted official control of her financial life to a fraudster.
Marie learnt a total stranger calling herself Julie had forged a form and been granted lasting power of attorney over all Marie's affairs.
"Julie" then used that power to try to take her home.
The Office of the Public Guardian, the government body that approves such applications, says such cases are rare.
"It has been my home, I love it to bits," Marie told BBC Radio 4's You & Yours.
"I feel incredibly fortunate to have this, and I was very angry that somebody had tried to take it away from me."
Marie, who owns her flat, went to care for her mother during the Covid-19 pandemic, leaving her own property empty.
The first she heard about the fraud was when the freeholder contacted her to say someone had tried to sell the flat.
When Marie got to her home, she found someone had broken in. "They rocked up in broad daylight and just drilled off the locks, they were that bold," she said.
"That was the moment I began to feel very scared."
She discovered that the solicitor's firm dealing with the sale of her home had become suspicious, asking for a doctor's note confirming that Marie did not have capacity.
"When asking for the documents, and pushing, nothing was forthcoming," explained Nicola Nolan, a conveyancer at Versus Law in Manchester.
"It was the geographical location as well, the fact she's down south and we were up north. Why use us?" The firm decided it did not want to act for the client and the sale did not go ahead.
The fake sister, Julie, had presented the solicitors with a genuine lasting power of attorney document, showing she had the right to sell Marie's house, and requesting that the £280,000 from the sale be paid into a bank account in the name of Julie.
Julie had also provided the solicitors with proof of ID - a driving licence with her name and picture, and two bank statements.
BBC Radio 4's You & Yours has obtained these documents. The lasting power of attorney document is completely genuine, but has multiple factual inaccuracies, fake names and the signatures appear as though they may have been written by the same person.
You & Yours visited the address on the bank statement and driving licence, in Sutton in south London, but it appears that the individual called Julie is no longer living there. It is not clear if Julie is the mastermind of the fraud, or if there are others behind it.
If solicitors had not spotted inconsistencies, Marie's home would have been sold without her knowledge.
'Scandal of huge proportions'
The Office of the Public Guardian investigates thousands of safeguarding cases every year, where individuals raise concerns that a lasting power of attorney is being misused or abused. In some cases the person named as the attorney is stripped of that power.
However, You & Yours has discovered that the same resources are not being directed at cases of fraud, where an application is entirely false. The government body does not use any fraud detection systems to cross reference the identities on applications, and currently employs no trained fraud investigators.
The Office of the Public Guardian told the BBC in a statement: "When fraud is committed it is extremely distressing and we act quickly to investigate and remove these from the register.
"We intend to introduce further safeguards against fraud and abuse. These include more direct inquiries with those creating the lasting power of attorney."
It confirmed that Marie's lasting power of attorney had been removed from the register and that the police had been informed.
David Lammy, who until recently was shadow secretary of state for justice, called the findings "a scandal of huge proportions".
The MP said: "A lasting power of attorney is a dramatic legal act, it's taking control of a human being's affairs, and it's extraordinary that legal protections are so weak that fraud can take place."
Mr Lammy called for a "root-and-branch" review of the system to ensure it was not exposing some of the most vulnerable people in society to fraud.
You & Yours also approached the Secretary of State for Justice Dominic Raab for comment.