21-year-old Kelly Noble has been found guilty of the manslaughter of Emma McLoughlin in Laytown, Co Meath, on 2 June last year.
The jury at the Central Criminal Court returned a verdict of not guilty on the charge of murdering the 19-year-old. Noble had denied the murder of Ms McLoughlin.
She had earlier been found guilty of producing a knife in a manner likely to intimidate or inflict serious injury.
The jury of seven women and five men took just over four and a half hours to find Noble guilty of manslaughter.
To bring in the manslaughter verdict they had to accept that she acted in self-defence using the amount of force she believed was necessary when she stabbed Ms McLaughlin in the chest or that she was provoked and lost control of her actions.
Noble showed no reaction as the verdict was announced.
She was remanded in custody and will be sentenced on 14 May.
Ms McLaughlin's family said they had no comment to make.
