Marianne Smyth (51) is serving a five-year prison sentence in a Los Angeles jail for grand larceny after also duping television producer Johnathan Walton into giving her thousands of dollars.
Mr Walton also believes Smyth may have duped 26 people here of around £380,000 during her time in Northern Ireland working as a mortgage adviser before moving to LA.
The PSNI is said to be investigating the claims.
Smyth is also accused of operating a fake GoFundMe page that used an image of her estranged late daughter.
Her story featured in a new ABC News documentary, The Con, which aired in the US this week.
After realising he had been scammed, Mr Walton (46) spent several years investigating Smyth's background and her dozens of other cons, which included once posing as Friends star Jennifer Aniston, going by multiple names and regularly changing her appearance.
Mr Walton, who produced American Ninja Warrior, worked with authorities until Smyth was eventually jailed for five years on grand larceny but her sentence has been reduced due to overcrowding.
She is due for release next February and could face extradition to stand trial in Northern Ireland where she previously lived for nine years, according to documents seen by The Sun.
Mr Walton told the newspaper: "After I realised I was conned, I went to police who kind of laughed at me at first and turned me away and said, 'This is not a crime'.
"So I started my own investigation and I hired private detectives all over the country.
"I did background checks and found out she had frauds and felonies in various states and I started a blog," he added.
"And as soon as I started my website, using every version of her name I had heard of, victims started contacting from all over the country from Florida, Tennessee, New York, Michigan, California, different places in Los Angeles.
"Eventually police started investigating her and she was jailed in 2019. And then one day I got a call from a police detective in Northern Ireland, in Belfast, who told me he'd been looking for Marianne Smyth for almost 10 years.
"They told me they believed she had been running these scams on 26 people to the tune of $500,000."
Mr Walton first met Smyth in 2013 and she managed to convince him she was due to inherit €5m from a family trust, describing her roots as "Irish royalty".
"She entered my life like most con artists enter people's lives - she offered to help. That's a big foothold. That's a big way in for a lot of cons," he said. "They want to help you make money or they want to help you find love."
Smyth convinced him to pay her rent during her case for stealing $190,000 from Pacific Islands Travel in LA, which she claimed was a set-up.
Mr Walton believed her tale and paid her $4,200 bail, which she reimbursed.
Following her conviction, Smyth told him that if she paid back $54,000, she would not have to serve jail time, so he lent her the money.
After discovering her deceit, Mr Walton engaged a private detective to find out the truth, which was that she was born in Bangor in the US state of Maine, not Ireland, and grew up in Tennessee.
Around 2001, Mr Walton says Smyth had moved to Northern Ireland after meeting a man from here online and worked for a mortgage firm.
He claims that police here have been investigating over 20 possible instances of fraud and have been in correspondence with a detective about the case.
A spokesperson for the PSNI said yesterday: "Police are revisiting reports of alleged fraud that occurred in 2009.
"As this is an ongoing investigation it would be inappropriate to comment any further."
The UK Home Office was also approached for comment.
This week's TV documentary also heard from Smyth's ex-husband Jeff Welch who accuses her of using an image of their late daughter Courtney on a fraudulent GoFundMe page, which has since been shut down.
Courtney, who was estranged from Smyth, died from cystic fibrosis in 2012 when she was in her early 20s.
Mr Welch said: "'Seeing this GoFundMe page - there was a picture of my daughter.
"[Smyth] had raised over $16,000 telling people she had a sick child. That made me sick to my stomach.
"I can't believe that somebody would do something like that."