Marjorie Mills put thousands of pounds into a Post Office account after she was attacked in her Edinburgh home.
However, amateur fighter Nadeem Amjid, 26, helped himself to her cash when he was working at the city's Colinton Mains Post Office.
His 19-month long scam was only rumbled after Mrs Mills's daughter checked her financial statements in May 2012 and discovered that the nest egg had been depleted.
Mrs Mills told her relatives she had been visiting the post office but had only been withdrawing £50 at a time.
Police were notified and an investigation was launched, which discovered Amjid had helped himself to a total of £33,646.
Amjid pleaded guilty to fraud at an earlier court appearance. Sentence had been deferred to allow Sheriff Paul Arthurson, QC, to obtain reports about his character.
Yesterday, after hearing how Amjid, of Edinburgh, stole the cash to fund a gambling problem, Sheriff Arthurson decided to send the first offender to prison.
He said: "Taking into account the nature of the crime, the age of the complainer and the fact that the complainer is vulnerable, the only disposal available to me is to impose a custodial term.
"You will go to prison for 20 months."