Just as she was about to go on trial for murder, mother-of-two Margaret Henderson-McCarroll pleaded guilty to manslaughter.
The 31-year-old was to have gone on trial at for murdering Mr Girvan, 67, in his home in Greenisland.
She said she was "not guilty of murder, but guilty to manslaughter on the grounds of diminished responsibility".
A Crown barrister said the prosecution accepted the plea of Henderson-McCarroll, who has a long history of drug addiction.
She also pleaded guilty to eight other charges resulting from the killing including:
The judge then remanded her back into custody while pre-sentence reports are compiled before sentencing next month.
In a bail application last November, the court heard that Mr Girvan's body was discovered tied up and seated inside his home on Station Road, where he collected antiques and jewellery, in January 2016.
He had stab wounds to his chest and his shorts were round his ankles.
A woman has admitted the unlawful killing of pensioner Eddie Girvan last year.