Const. Dany Lacoursière of the Montreal police said the confrontation began when a noisy group emerged from a bar on Dollard Street near Lithuania Street just after the bar closed at 3 a.m.
Lacoursière said the woman’s son went outside to tell them to be quiet, and was assaulted by part of the group.
“His mother saw the aggression, took a sharp object and went down,” he said.
Both the woman’s son and his 21-year-old aggressor — who was stabbed in the upper body — are in hospital.
The woman is being questioned by police.