Mrs Franks was forced to take Mr Folan, now 70, to court over the right to organise the funeral arrangements.
But a four-day hearing at Leeds county court ended with the judge siding with Mr Folan – and Mrs Franks and her relatives were left with a £200,000 legal bill.
This resulted in them handing their £175,000 half-share of their mother's house to Mr Folan, topped up with their savings.
Mrs Blass was eventually buried in an unmarked grave in a town she had no connection with. None of her relatives were invited to the funeral.
Mrs Franks, who is now campaigning for a change in the law to protect people like her late mother, said: 'It is impossible to describe the level of shock and distress that we felt on learning of the marriage.
"When I found out I felt like my knees were buckling and that I was going to faint. I cannot state too strongly how devastated my mother would have been if she had known that the marriage would disinherit her children."
A complaint to police led to a file being sent to the Crown Prosecution Service to consider a 'forced marriage' charge, but lawyers decided against prosecution.
Mr Folan met Mrs Blass in 2011 – the year she was diagnosed with vascular dementia.
Having struck up a conversation as he walked past her house in Leeds, he moved in with the widower a month later.
Mrs Franks and her husband, who lived next door, were worried about Mr Folan but could do nothing about the relationship as there was no evidence of mistreatment.
Mrs Franks said: "Mum never seemed to know he lived there. She was asking, 'what is his name? Where did he come from?'"
The couple married in Blackpool in October 2015.
The only witnesses were Mr Folan's son and a member of his pub quiz team.
"[He] never told anyone about [the marriage], because, I suspect, he had found out that there is a gap in the law," Mrs Franks said.
She contacted Blackpool registrars to find out why no concerns were raised, only to be told Mrs Blass seemed happy on the day.
Mr Folan still owns the house but no longer lives there. He could not be reached for comment.
Earlier this year he dismissed the accusations, saying he and Mrs Blass had a 'loving' relationship and insisting she had the capacity to go ahead with the marriage.
A Crown Prosecution Service spokesman said: "We reviewed this case carefully and concluded that there was not sufficient evidence for a realistic prospect of conviction."