That was the "chilling insight" Marcela Castaneda​ had about the fate of her volatile relationship with her fiance, Gregory Peck, the NSW Supreme Court has heard.

On the first day of her trial on Wednesday, a jury was told Ms Castaneda fatally stabbed Mr Peck in 2013 after he choked her during an argument about postponing their wedding.

The 33-year-old has pleaded not guilty to murder, and is arguing she acted in self-defence, after a long history of domestic violence.

Her barrister, Philip Strickland, SC, said there had been several violent incidents over the course of their five-year relationship, and Mr Peck was known to have become aggressive after drinking alcohol.

After the stabbing at the couple's home in Cecil Hills on February 22, 2013, Ms Castaneda was taken to a police station, where she called her former husband for support.

The jury was told they will hear evidence Ms Castaneda told her ex-husband about what happened.

"I was on the computer and we were arguing about the wedding – I wanted to call it off and he started choking me," Ms Castaneda is said to have told her ex-husband.

"When he let go, I got up and went to the kitchen, I was really scared.

"All I wanted to do was to keep him away. He came towards me and I was trying to keep him away.

"Somehow the knife ended up in his shoulder."

Mr Strickland said that, in 2012, Ms Castaneda wrote Mr Peck's aunt a Facebook message saying he had choked her and pulled her hair.

A former girlfriend of Mr Peck had written a message to Ms Castaneda warning her of his violence, saying he had once dragged her by her hair, thrown her out of the house while she was undressed and called her a bitch, the court heard.

When an apprehended violence order was taken out against Mr Peck on behalf of Ms Castaneda in 2012, she told police she was afraid of what he might do to her, and police believed her fears, Mr Strickland said.

"That's what she knew at the time of the incident. What had happened to her, and what had happened to his previous girlfriend."

Prosecutor Patrick Barrett said the Crown would need to prove that Ms Castaneda intended to kill or seriously hurt Mr Peck that night.

He said Ms Castaneda had told ambulance officers, police and her ex-husband different stories about the night of the stabbing.

She had also been violent to Mr Peck, Mr Barrett said.

"I expect you'll hear some evidence about previous occasions … where there had been arguments or events that have resulted in use of some force or some violence by Mr Peck, or occasions where there has been some force or some violence during arguments by the accused," Mr Barrett said.

The trial continues before Justice Helen Wilson.