Convicted killer Helen Milner has lost her bid to challenge her murder conviction in the Supreme Court.
But the court said another application for an appeal could be made if further investigation reveals her husband, Phil Nisbet, may not have died from a drug overdose.
Milner was sentenced to life in prison for killing Mr Nisbet with an overdose in 2009 and making the death appear to be suicide.
She appealed against her convictions for murder and attempted murder on the grounds the Crown had not proven the drug had could have been administered without Mr Nisbet's knowledge.
The drug promethazine hydrochloride, or Phernergan, tastes bitter in lethal quantities.
The Court of Appeal dismissed the appeal, saying it was not an element that needed to be proven beyond reasonable doubt.
Milner appealed to the Supreme Court on the ground that the verdicts were unsafe unless the Crown could prove beyond reasonable doubt how the drug was administered.
The Supreme Court upheld the Court of Appeal's view that the method of administering the drug did not need to need to be proven. It was enough that the judge directed the jury to be sure that Milner had drugged Mr Nisbet without his knowledge.
However, during the appeal process a pathologist had contacted Milner with doubts that promethazine was the cause of death.
The Court was asked to grant leave to appeal on the basis that the new evidence would have raised a reasonable doubt if put before the jury.
But the Court said the expert opinion was tentative and did no more than raise lines of inquiry into other explanations for the death.
Should more evidence emerge, an application for leave to appeal could be considered.
