Antrim Crown Court in Coleraine heard today that Hazel Stewart's defence lawyers need time to consider the statement made by dentist Colin Howell, who has already been sentenced to life imprisonment for the two murders.
Howell, 51, from Castlerock, Co Londonderry, will be told next Monday how long he has to serve.
Her defence layer Paul Ramsey QC said he would now consider the lengthy statement from Howell and the trial would be unlikely to start before Christmas.
He said there was a ferocious amount of detail to be examined and medical and psychiatric records.
Mr Justice Anthony Hart said he had only recently become aware of the additional evidence and that he would set the tariff for Howell's life sentence on Monday.
Mr Ramsey added: "This development means that matters may have to be put back. I would have thought it will be unlikely that we could start the trial before Christmas.
"The defence will need that time to absorb the material consequences that arise from this."
Mrs Stewart's children Andrew and Lisa were in court.