But while she wanted to move on with her life, the threat of decapitation on May 4 last year and giving evidence against Hirst at trial haunted the teen.
At the end of November, a few weeks before her ex-boyfriend was jailed on charges of threatening to cause grievous bodily harm and assault, Katie died of a drug overdose.
Her parents, Bill and Susie Burt, were at the Dunedin District Court earlier this month to see Hirst locked up for 20 months.
Mrs Burt stood in court to speak of the crushing impact he had on her family.
"I just don't feel he's remorseful at all," she said.
"He's not even tried to check up on his daughter ... or contact the family to show us condolences."
She wanted to make it clear, too - Katie's death was the result of an accidental overdose, not suicide.
While this was yet to be confirmed by the coroner, the couple were convinced.
The May incident and subsequent court case had left Katie depressed and suffering panic attacks but she was not suicidal, Mr Burt told the Otago Daily Times.
His thoughts on the matter were clear.
"It shouldn't have been Katie in that coffin. It should have been that b*****d," he said.
Hirst met the victim when she was 15 and staying in a Dunedin flat with friends.
Katie tentatively told her mum she was in a relationship and shortly afterwards, even more reluctantly, the pair disclosed they were expecting a baby.
"I was completely gobsmacked," Mrs Burt said.
She and her husband went straight to police. For them it was statutory rape by a man seven years older than their daughter.
The case almost made it to trial but in a move the Burts say was cooked up by Hirst, their daughter changed her Facebook profile so it appeared she had been misleading him about her age.
Police pulled the charges and so began three years of turmoil.
Katie lived with her parents during the pregnancy but once she had moved out, her bond with Hirst blackened.
There was drinking and arguing.
There were drugs and mind games.
They were "on and off", but never truly off.
"We tried everything to get her away from him but he just kept coming back," Mr Burt said.
"We couldn't do anything," Mrs Burt added.
"The more you nagged her, the more she dug her heels in."
When Katie got into trouble, she would call her parents for help and they would duly rush out to the South Dunedin address, every time fearing the worst.
"We used to cringe at night when the phone went. It'd be like 'what's happened now?'" Mr Burt said.
On May 4, the phone rang again. Katie had shut herself in a bedroom, Hirst was on the other side of the door with a knife, telling her to come out.
Earlier in the day he had been arguing with people on the street.
Hirst tried to set his pit bull on them but Katie dragged the dog back indoors.
Angry she had not backed him up, the 26-year-old grabbed her by the singlet and repeatedly pushed her into the door.
Later, with more alcohol inside him, Hirst accused his then girlfriend of sleeping with a friend of his who had just arrived from up north to stay with them.
He then made the chilling threat to decapitate the teenager and went to the kitchen for a knife.
She hid in the bedroom and called police after alerting her parents. Hirst was arrested and Katie left him for good.
Judge Michael Turner came to the same conclusion as the Burts about the man.
"I detect no acceptance of responsibility for your actions or any remorse for your behaviour, or insight into the effect of your conduct on others," he said at sentencing.
"You were her partner. She was entitled to be treated with love, respect and dignity. You did anything but."
Sitting in his Musselburgh home, Mr Burt swelled with pride as he recounted how staunchly his daughter gave evidence against her ex.
But despite being clear of him, the trauma she had sustained was undeniable.
Did the relationship change her?
"Yes," Mrs Burt said, emphatically.
"Completely."
Katie was frightened of living on her own and scared to go out in public, her mother said.
They described her as "a really happy-go-lucky kid", a talented musician who got a piano scholarship from primary school.
They refused to romanticise their daughter's memory, though.
"She wasn't a perfect kid," Mrs Burt told the ODT.
"She had a few troubles at school ... they didn't like her hair colour or body piercings."
The Burts smiled as the memories came.
"She had a good heart. She had a bloody good heart," Mr Burt said.
Katie was determined to move on with her life and resume her studies for the sake of her daughter's future, as much as her own.
Her parents recalled her pride at attaining a barista qualification, which she saw as a ticket to the world.
It was supposed to be the first step towards turning her life around and Katie had moved to a small flat on Elm Row to escape her "dramas".
But after 10 days there, and some unwanted attention from another older man, who was nearly twice her age, it happened.
Police sat her parents down at work and told them their daughter had overdosed on morphine.
"I didn't know what to say or do," Mrs Burt said.
The pain is still raw for the couple but they have the sweetest possible reminder of their daughter in front of them every day - their 3-year-old granddaughter, who now lives with them.
But it had not come without the odd curly question.
"She sort of understands ... I told her her mum's an angel," Mrs Burt said.
"Now and again she will say 'I want to see mummy' or 'I love my mummy' and you don't know what to say."
Things will be relatively simple while Hirst is in prison but if he wants to make a bid for custody of the child once he's released, there will be steely opposition.
"The grand total of what he's done for her is one pack of nappies, a big ugly stuffed toy and a tattoo on his neck," Mrs Burt said.
In the meantime, there would be no closure until the coroner's report came back.
"Just to say Katie didn't kill herself, that's what I want," she said.
When it came to Hirst, the couple were in agreement.
There would be no forgetting and no forgiveness.
"It's hate," Mr Burt said.
"It's an unhealthy hate. There's so much anger there."
rob.kidd@odt.co.nz
