Lisa Doe, 21, of Denmark Street, denies murdering Patrick Garwood following a drugs binge on August 23, 2001.
She told the court that she met Mr Garwood on the Warren housing estate a week before his death.
Doe took homeless Mr Garwood, originally from London, back to her third floor apartment.
Patrick Curran, defending, asked Doe if Mr Garwood was prone to mood swings.
She said: “Yes. We would be chatting and then if I could not give something to him, like beer or drugs, he would shove, push or get verbally aggressive.”
She added that when she asked Mr Garwood to leave a few days later, he refused.
The court heard that on the morning of the alleged murder Doe had left Mr Garwood in the flat while she went shopping with her younger sister, Karen, 18.
During the day the pair had bought Valium, temazepam, methadone, heroin and crack cocaine.
The jury was told that shortly after the sisters returned to the flat Mr Garwood left to get a cigarette.
Doe said she spent much of the day smoking crack cocaine and sharing a two-litre bottle of cider with Karen.
When Mr Garwood returned Doe said that she talked to him for about 20 minutes outside the flat.
She said: “When I asked him about a rumour that he had stabbed his ex-girlfriend or wife, he became aggressive.
“Patrick went to walk off and he turned around and kicked me in the face.”
Mr Garwood, Doe claimed, stepped over her body and went into the front room.
“I got up and followed him into the front room,” said Doe.
“I was shouting to Patrick to get out of the flat. He was shouting abuse stuff like he was not going to leave. Then I just remember seeing the knife in his hand.”
Mr Curran asked her what was going through her mind at the time.
A sobbing Doe replied: “ I was terrified. I just wanted him out of my flat. I was doing anything I could to get him off me. He was punching and shoving me, kicking me, doing anything.”
She added that she did not intend to cause Mr Garwood serious injury. She said: “ I was in a hysterical state because I was fighting for my life.”
Under cross examination Michael Bowes, prosecuting, asked Doe if Martin Beck, who had been in the flat at the time of the alleged incident, had been correct in saying that he saw her arm coming in a downwards motion. She replied: “He would have seen both our arms punching.”
Mr Bowes added: “He then said that he (Mr Garwood) was stumbling backwards towards the TV and then go at an angle towards the radiator and slump down. Martin Beck said that when Patrick was on the floor he was saying ‘Lisa, Lisa’.”
Doe replied: “No, he did not say anything.”
The prosecution claims that Doe intentionally stabbed Mr Garwood, 39, three times with a large knife, which she claimed he had threatened her with.
Neighbours later saw Doe, her sister and a friend dragging his body downstairs.
A post mortem revealed Mr Garwood died from a 10cm long stab wound through his heart. The case continues.