Sheriff Annella Cowan said the children of Theresa Riggi were let down by the justice system, which did not act quickly enough to prevent their deaths.
Riggi stabbed her young sons and daughter, the day after she failed to turn up for a divorce court hearing. A court had ordered them to be urgently taken into care to keep them safe.
Sheriff Cowan made the claim during a separate child custody case in Aberdeen where she took action to protect a child before the mother had been given the chance to give evidence.
Insisting there were no delays, Sheriff Cowan said: "I was conscious that the legal system had, in the preceding month, patently failed to protect three children when court orders had not been acted on expeditiously."
Last week a more senior judge overturned her decision after ruling it infringed the mother's right to a fair hearing.