SHE stabbed her older brother once through the heart, ending his life and changing the course of her own forever. Caroline Brennan (19), who has shown considerable remorse for killing her violent and abusive brother Michael (22), escaped a jail sentence last week after being handed down a five-year suspended sentence for her crime.

Her father pleaded with judge Paul Carney for leniency. The family has suffered other untimely deaths, he told the courtroom quietly, and jailing his daughter would only add to their pain while they were still grieving the loss of their son.

The teenager now joins a growing list of women convicted of killing men who have evaded spending time behind bars. In 2001, Galway woman Kathleen Bell stabbed her brother-in-law to death with a potato peeler and was tried for his murder in 2003. She was convicted of the manslaughter of Patrick Sammon, her late sister's husband with whom she had started a relationship. She stabbed Sammon, who had hospitalised her 51 times following violent attacks, when he insulted the memory of her dead sister. She was handed down a suspended sentence and told to undergo therapy.

Last year, Anne Burke (56), of Ballybrittas in Co Laois, admitted hitting her husband Pat Burke (55) over the head with a hammer while he slept, but denied murdering him at their home on 19 August 2007. After listening to evidence over two days that detailed the pitiful existence that was Anne Burke's life at the hands of her domineering and violent husband, a jury found her not guilty of murder but guilty of his manslaughter on the grounds of diminished responsibility. She has yet to be sentenced but a legal source said it was unlikely she would be imprisoned, given her psychological problems and her husband's history of violent behaviour.

All are tragic cases, both for the men involved and the women who took their lives. But a pattern in the judicial system is emerging whereby if a man killed by a female relative or spouse was violent and abusive, the woman responsible often escapes being jailed.

There have been high-profile exceptions to this, most notably Charlotte and Linda Mulhall, convicted of the murder and manslaughter respectively of Kenyan Farah Swaleh Noor.

The circumstances of what led Caroline Brennan to kill her brother have shed light on yet another case of how continuous bullying, threats and physical attacks resulted in an unnecessary killing.

It started out as an average night out for Caroline Brennan. Originally from Castlecomer in Kilkenny, but now living in Dublin, she went to the local pub The Coalmine Inn in her home town with her boyfriend Keith Byrne and her friend Melissa Fox on 29 December 2008.

Her brother Michael was having a party in their uncle's house across the road from the pub on Barrack Street, which Caroline initially had no intention of attending. Michael had been living with his uncle Ollie Nolan since his parents were forced to ask him to move out of the family home.

Nolan, who suffered from mental health problems, has since died.

"He just kept getting worse and worse; he was bullying me. Michael was just very, very violent... they put him into rehab twice; he didn't want to be there," Caroline told Waterford Central Criminal Court during emotionally charged testimony on Tuesday.

"He was kicked out of the house because he was very violent towards me and the younger ones."

Caroline and her boyfriend Keith got into an argument in the pub after he mistakenly believed she was flirting with another man. The young couple were also in disagreement about attending the party in Ollie Nolan's house – Keith wanted to go but Caroline did not, knowing that a meeting with her brother could spark trouble.

The fight between the pair escalated. Keith eventually punched a wall and Caroline ordered him to move out of the flat they shared in nearby Love Lane.

He went home and duly began packing his bags. He then got into his car, saying he was going to drive to Dublin where his family lived. The couple then reconciled. But Keith insisted he was still going to the party at Ollie Nolan's house, as he'd promised Caroline's other brother Thomas that he'd meet him there. Caroline still didn't want to go, she told the court, but also didn't want her boyfriend going alone. "I was afraid for the two of us," she said. For that reason, the teenager armed herself with a knife. When Keith Byrne saw her bringing the knife, he said: "'You don't need that, I'll take care of you.' She said, 'you'd never know what he'll do."

Soon after she arrived at the party, Caroline was in conflict with her brother. She had found out earlier that night that he had started using heroin and confronted him. He became furious with her, locked her in the bathroom and forced her to apologise to his friend who she accused of providing him with heroin.

Deeply upset, Caroline then left the party with Keith and the pair were sitting outside in his car when they heard a loud scream. Michael's girlfriend Lisa Peagram then emerged sobbing from the house. Michael had punched his girlfriend, "grabbed her by the throat" and threatened to kill her.

Caroline comforted Lisa and invited her to come away and stay with them at their flat. "I told her it's not safe; to come stay with me and Keith," Caroline told the court. But Lisa had left her mobile phone and bag in the house and Caroline ventured back inside to fetch her belongings.

Michael Brennan, high on a cocktail of drink and drugs, was acting increasingly erratically. Once inside, Caroline took "a sniff" of cocaine offered to her by one of her brother's friends, but soon tried to leave the party.

"Everyone was bonkers on drugs and drink," she said. Her brother was blocking her from leaving with his arm and shoulder when she produced the knife and stabbed him once in the chest. Breaking down in tears in the witness box, she told the court she hadn't meant to stab her brother and certainly did not intend to kill him.

Caroline's family have forgiven her for Michael's killing, and her brother's partner Lisa Peagram has said she's glad that the teenager wasn't jailed for her actions. She described Michael as an entirely different person when under the influence of drink and drugs.

In his victim impact statement, Bill Brennan said that if his daughter were to walk from court, it would put an end to the family's suffering.

"I would appeal to you, judge, to give us a chance to take her home and get her through her education," said the father-of-eight.

"It's been a very, very rough four years for the family; it could all end here today."

Justice Paul Carney effectively granted the family's wishes by suspending Caroline Brennan's five-year sentence because of the "highly unusual circumstances" of the killing, adding: "She will have to live the rest of her life with a conviction for fratricide."