Ex-florist Stephanie Todd, 57, caused suspicion by trying to change Philip Wall’s will to become the main beneficiary when he intended to leave his money to the Cats Protection charity.
The solicitors’ firm that held power of attorney over Todd’s profoundly deaf and occasionally confused victim became suspicious when she tried to switch legal firms, and they called in police.
By that stage she had regularly siphoned off up to £300 a time from cashpoints, carefully staying below the £1,300 a month the former GPO engineer received in his pension.
Judge Stephen Ashurst, sitting at Teesside Crown Court, jailed her for two and a half years and said she was in disgrace.
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Mr Wall, from Richmond, North Yorkshire, was a modest, frugal, independent man whose late wife loved cats and made him promise to leave his money to a charity that helped them, the judge said.
The childless victim thought Todd was charitably disposed towards him, and Todd cynically portrayed herself as a “saint” by helping him, the judge said.
Judge Ashurst told her: “You were a forceful woman in your 50s, who exploited that position to exert influence on a very old man.
“He was 98 when he died, knowing that someone who he had trusted had stolen from him.”
Todd and Mr Wall had a chance meeting in August 2013 and she befriended him, swiftly taking over the role of cleaner and helping to look after him.
Shaun Dryden, prosecuting, said: “Essentially she tried to help him following that accidental meeting.
“What becomes clear, in a very short space of time, is that this defendant made every effort to rearrange Mr Wall’s financial affairs.”
She used his bank card to withdraw more than £46,000 from his bank account over three years.
Todd sometimes used the card at night in Darlington and in Oxfordshire - clearly not the actions of an elderly and frail man, the court heard.
He died in February, having seen Todd convicted of theft in December.
Her sentencing was delayed after she had a stroke shortly before the jury came back with a verdict and she now uses a walking frame.
A month before his death, Mr Wall made a victim statement to police, saying: “I trusted Stephanie Todd and I fear she has betrayed that trust by stealing money from me when I was in a vulnerable position.
“Since being told of Stephanie Todd’s actions I have been constantly anxious and I have worried over this daily and I found it difficult to trust people.
“I am 98 and the fact someone has stolen from me has marred the final years of my life.”
Todd, from Shute Road, Catterick Garrison, North Yorkshire, stood as a Ukip candidate in the 2015 General Election, having defected from the Tories in 2013, and was a councillor on Richmondshire District Council.
Simon Perkins, defending, said: “Miss Todd is remorseful for her conduct. She accepts she has thrown away 57 years of good character.”
Detective Constable Nicola Hancock, from North Yorkshire Police’s Economic Crime Unit, said: “Todd preyed on an elderly and vulnerable man in his time of need, she gained his trust and proceeded to steal thousands of pounds, as well as convincing him to change the details of his will.”