The scheme involved a series of transactions between 2007 and 2010 which deceived lending institutions into approving mortgage applications that contained false information and supporting documents.
Devoy, who was considered the ringleader of the group involved, was found guilty of 17 charges in relation to the scheme in June last year.
She was sentenced to five years jail with a minimum period of imprisonment of two years and six months.
While Devoy appealed her conviction and sentence to the Court of Appeal on the grounds that her trial lawyers made errors, three judges have now overturned her appeal.
Court of Appeal Justices Rhys Harrison, Murray Gilbert and Sarah Katz said the evidence of Devoy’s guilt was overwhelming.
"She has no rational basis for continuing to deny criminal liability," they said in their decision.
The Court of Appeal judges said both Devoy’s lawyers discharged their obligations with skill and care in demanding circumstances, while the judge had considered the evidence in meticulous detail.
"Devoy was the beneficiary of a very fair and competent judicial evaluation of charges to which she had no credible defence," they said.
"She cannot possibly claim that justice has miscarried in her case.”
In the original trial, Judge Brooke Gibson said there was a high level of "pure deceit and dishonesty" in Devoy’s offending.
She also told Devoy there was a complete absence of remorse on her part and that her protestations of innocence verged on fantasy.
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