"I didn't have anything to tell them back then. Things that they had asked me, because I had not been with him that long, I would say no to," she told Stuff.
"If they asked me those questions again I suppose I would have different answers."
The woman, who cannot be identified for legal reasons, says her partner's vehicle had been of interest to police after the murder.
DNA samples were taken from it and tested.
The woman told Stuff that when her ex-partner became intoxicated he would joke about being the killer.
"He used to say it jokingly, well, I suspect it was jokingly, when he was drunk."
The man often appeared to know more about the case than what had been released publicly, the woman claimed.
"I remember that conversation. It's a conversation that has always stuck in my head."
In 2010, after a documentary on the cold case aired on television, the woman says she contacted Detective Inspector Greg Williams, who was then in charge of the case.
However, after raising her concerns over her ex-partner's involvement, she felt that the senior police officer "wasn't listening to her".
Detective Inspector Greg Murton has since taken over the cold case.
He told Stuff that he would not comment on the woman's allegations, saying the man had already been investigated.
DNA was still being tested and investigations are ongoing, Mr Murton said, adding that the woman was welcome to contact him.
Kirsty's father Sid, 64, died last Monday of cancer.
He was also a suspect in his daughter's murder but had always denied any involvement.
