There she "picked up the biggest knife in the butcher's block" before attacking Stewart, he said. Stewart was left holding a towel against the side of her own neck in the moments after the attack, according to recordings of 111 emergency calls played to the court.
Stewart's cousin Patricia Stewart, in one call, told a St John paramedic that despite the towel being pressed against the wound, blood was "everywhere" and running out her cousin's mouth and nose.
In the call's background, women can be heard crying and then confronting Browne.
Constable Samuel Sweetman arrived as the women threw a chair at Browne outside the front of the home and, leaving his partner to arrest her, went in to help Ms Stewart, who was sitting on a couch spitting blood.
Earlier, Webby said that in contrast to how it ended, the day had started brightly. Most of the women gathered were family or friends from primary school and had come to have fun and get their nails and lashes done, he said.
Browne arrived early in the morning with bourbon and vodka and became abusive as the day progressed.
When she called a fellow guest a "gang whore", the party's organiser and Stewart remonstrated and both got into altercations with her.
"How dare you, this is a family house, my nieces are here", Stewart told Browne, Webby said.
Immediately after, however, Browne grabbed the knife and struck Stewart in front of the other guests, including children, he said.
Stewart would die soon after, while Browne was arrested at the scene.
The trial has been set down for three weeks.
