Diana Butler, 32, from Doncaster, South Yorkshire, now faces a retrial.
Three judges, headed by Lord Justice Pill, ordered a retrial for Butler, who was convicted last December of murdering Roger Carlin at the couple's home in Wheatley, Doncaster, in July 1996.
The court gave the Crown Prosecution Service 28 days to draw up a new indictment against Ms Butler, who remains in jail pending a bail application next week.
The judges ordered a ban on further publicity surrounding the case.
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