Kerry Holden, 40, was sentenced to at least 18 years in jail after Luke Moran was stabbed to death at a house party in Nottingham in 2011.
She had gone to the Court of Appeal after it emerged another man, who lived nearby, had admitted to the crime.
But judges said the man was mentally ill at the time and had since retracted his confession.
Holden, of Farnborough Road, Clifton, Nottingham, was convicted in 2012 of murdering the 25-year-old after following him into a garden.
Her lawyers claimed the man's confession had made her conviction unsafe.
But Lord Justice Davis said the "purported previous confession" of the other man was "plainly unreliable and incapable of belief".
The court heard the man had been seriously ill with a form of paranoid schizophrenia when he spoke to police and, since he had become well again, had retracted the confession.
There had been no reason to suspect him at the time of the murder and his account of how he had carried it out was "vague", said the judge.
A mother has had her murder conviction appeal dismissed after judges rejected a 'rival' confession.