95-year-old Mary Hookham, of Whinmoor, Leeds, is the great-grandaughter of Sarah Chesham, who was dubbed 'Sally Arsenic' in the mid 19th century as she one of the most notorious female posioners of the era.
Sarah Chesham, 41, was the last woman to be put to death in England for attempted murder.
Mrs Hookham, nee Chesham, said she was pleased experts on BBC TV documentary Murder Mystery and My Family, which was screened this morning (Weds April 3) , had looked again at the case.
A retired judge came to the conclusion that the verdict was unsafe after two barristers re-examined the evidence.
Mother-of-two Mrs Hookham's youngest son Andy Greaves, 67, discovered Sarah Chesham was a relative while researching his family tree around three-years ago.
Mary Hookham, who is a great great grandmother, said: "I was astonished that we had a supposed murderess in the family."
After watching the BBC programme, Mrs Hookham, said she was pleased with the findings.
She said: "For someone to have to forfeit their life when they are innocent is very sad."
Sarah was first charged with murder in 1846, when she was accused of killing two of her sons and of poisoning another young child.
She was acquitted at the subsequent trials and returned to the tiny village of Clavering in Essex, but she could not shake the rumours of her guilt.
In 1850 Sarah returned to court, charged with the attempted murder of her ailing husband Richard and was found guilty.
On 25 March 1851, she was hanged in public before a crowd of thousands.
Barristers Jeremy Dein and Sasha Wass re-investigated the circumstances of Richard Chesham's death on behalf of Sarah Chesham's descendant Roz Powell.
Small traces of arsenic, which had been found in her supposed victims, are not uncommon in the human body.
Experts who reviewed the case for the documentary found that tests carried out at the time were inconclusive and that her 'victims' had most likely died from natural causes.