Molly Martens-Corbett killed her husband because she feared he would return to Ireland with his children, officials believe.
The unanimous second-degree murder convictions against Martens-Corbett and her father are set to cost the young Tennessee woman more than $1m (€850,000).
But according to sources in the District Attorney's office, Martens-Corbett (33) was afraid that her husband Jason Corbett (39) might not return from a family event in Ireland. Mr Corbett had two children from a previous marriage.
"Jason was due to fly back to Ireland for a family birthday party a couple of weeks after August 2," the source said of the weeks leading up to the 2015 killing.
"The evidence indicated he had told his family he was travelling with his children, Jack and Sarah. But there was no mention of Molly travelling.
"The jury certainly could have inferred that she was afraid the children might not return to the United States."
The source added that evidence indicated that Thomas Martens, who was also convicted of second-degree murder, was encouraging his daughter to consult with a lawyer about divorcing Jason.
"He did not consider it a good marriage. But she wanted his children and Jason had refused to sign adoption papers for her.
"It was not all sunshine and roses (in the marriage)."
The father and daughter are to lodge legal papers within days with the North Carolina Court of Appeals, to challenge their murder convictions.
Michael Earnest, Molly's uncle whose sister Sharon is married to Martens, said they were "devastated".
"In my opinion and in my personal life this is the most atrocious miscarriage of justice I have ever been a part of," he said.
Mr Earnest, a Federal employee who is part of the US Afghanistan Reconstruction programme, vowed the family will never stop fighting to prove their innocence and to show they acted entirely in self defence. But jurors in the four-week murder trial revealed they were convinced that callous Martens-Corbett actually attacked her husband while he was still asleep, and her father came upstairs to help finish the job.
Both father and daughter are now being kept in high security prisons outside Raleigh as they begin sentences of between 20 and 25 years for the murder of the Irish businessman.
The jury of nine women and three men unanimously rejected the self-defence argument and convicted them of second-degree murder.
Now, Martens-Corbett faces losing a $600,000 (€507,000) life insurance policy pay-out due on the death of her husband.
She was the main beneficiary of the policy taken out by Jason's employer.
The money, payable by a Maine-based insurance firm, has been kept in a trust fund since 2015.
Similarly, while Martens-Corbett was not mentioned in her husband's 2007 will, the conviction will effectively void any claim she may have to the luxury home he bought for $390,000 in 2011. There was no mortgage on the property.
Martens-Corbett will also lose any claim to the $80,000 (€67,000) worth of fixtures and furnishings at Panther Creek.
It is understood she had attempted to dispose of some items from the property but all were removed and placed in secure storage pending the outcome of the trial.
It is understood that all monies involved will instead be directed towards the estate of the Limerick man's two young children, Jack and Sarah.
Meanwhile, defence lawyers David Freedman and Walter Holton will review the trial transcripts and prepare their grounds for appeal.
All trial documents will not be available from Davidson County for at least 90 days. No North Carolina Court of Appeal hearing will take place before then.
The initial basis of challenge will be on an area of law or evidential problems - with the defence lawyers seeking a full review of the case.