Daphne Franks' says her mum Joan Blass was taken advantage of by a man 24 years her junior.
Mrs Blass was in her 80s when she met Colman Folan, and had been recently diagnosed with vascular dementia.
Appearing on GB News, Ms Franks told Gloria De Piero: "We'd been aware of the threat of this man for several years. We'd been to all the authorities and people didn't know what to do or just didn't perceive the threat."
When Mrs Blass died at the age of 91 in 2016, the family became aware that the pair had married.
Ms Franks added: "She died on Easter Saturday 2016, on Easter Tuesday, when everything opened up again after the Easter holiday, we got a phone call from mum's GP and he sounded really worried and he said: 'Daphne do you know your mother was married?'
Mrs Blass was diagnosed with vascular dementia in 2011
GB NEWS
Mrs Blass with her daughter Ms Franks
GB NEWS
"We had seen it coming, we had been to everyone and tried to stop it and got know where."
Ms Franks took Mr Folan to court on the advice of a solicitor.
The proceedings ruled in favour of Mr Folan as she was legally married to him.
Ms Franks expressed her devastation in the events that followed the proceeding: "As a result of that the man had a secret funeral after the secret marriage, we couldn't go we didn't know when it was.
"We tracked her grave down, it's in a town near Leeds, with which mum had no connection, the grave is unmarked."
She told Gloria that her mum "never knew she was married" and "she was wearing my dad's wedding ring until the day she died".
After Ms Franks' case concluded, families whose elderly relatives have fallen into similar predatory marriages have supported calls for changes in the law.
MP for Leeds North East Fabian Hamilton has been inundated with enquires from families since he first mentioned the issue in Parliament in 2018.
Mr Hamilton presented a private members' bill on the issue to the House of Commons in 2018, but is yet to meet with the Registrar General to talk through proposed changes.
The issue of predatory marriage was raised by Mr Hamilton once again at Prime Ministers's Questions in June last year, where he called for an update to the "19th century" marriage legislation that currently permits it.
Earlier this year, Ms Franks welcomed a round-the-clock helpline by The Hourglass charity, which is set to help those affected by elder abuse.