Shaking and fighting back sobs, Marcela Castaneda stepped into the witness box and re-lived the final "terrifying" moments before she plunged a kitchen knife into her fiance's chest.
And then she told the Sydney court how she grabbed her phone, dialled triple zero and begged the operator to send an ambulance right away.
"I was panicked. I was worried about Greg," Castaneda told her NSW Supreme Court manslaughter trial on Wednesday.
She said the police constable who questioned her in her western Sydney home that night had to keep reminding her not to look back at her long-time partner Gregory Peck as he lay dying nearby.
"I heard him. He was still alive ... I was thinking, hoping, he was OK," the 33-year-old said.
The woman fought back tears during hours of evidence, and at one stage had to take a break after she was overcome by emotion.
Castaneda testified that on the night of February 22, 2013, she called off her wedding to Mr Peck, telling the American aircraft engineer their four-and-a-half-year relationship was over.
"All of a sudden I could feel his hands around me," she said.
"I could feel pressure around my neck and I was struggling to breathe ... I couldn't scream."
She said it was not the first time Mr Peck had choked her, but her fear intensified when he tried to follow her into the kitchen.
"That scared me, because he'd never come after me before. So then when I saw the knife, I just grabbed it," she said.
Castaneda gave evidence she tried to lead Mr Peck from their home at knife-point and got as far as the patio, where he swore and "lunged" at her in the doorway.
"I thought he was going to hit me," she said, as family members sitting in the public gallery wiped away tears.
Then she stood and demonstrated how she held up one hand in a "stop" motion and jutted forward with the other - the hand that held the knife.
Castaneda was initially on trial for murder but found not guilty on that charge after Justice Helen Wilson told jury members the evidence before them was not capable of proving murder.
Crown Prosecutor Patrick Barrett has challenged Castaneda's account, arguing on Wednesday that Mr Peck had not threatened to hit her in his last moments.
"Ms Castaneda, I suggest to you that you stabbed him because you were angry," he said.
The accused woman replied: "No, that's not right."
Mr Barrett also questioned why she did not simply shut Mr Peck out of the house.
"Why didn't you shut the door when he said that?" he asked.
"Because shortly after he lunged forward. I didn't have a chance," Castaneda said.
The trial continues.
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