The crimes shocked the small seaside community but for those who knew the killer they weren't a shock.
In fact, five years before carrying out her quiet double murder, Haines bragged to a partner about being able to do just that.
The jury in her murder trial heard how, in 2009, while watching crime show CSI, she remarked about how killing a person would be fast work and undetectable, ABC News reported.
"It's easy," she said. "Inject with insulin ... because the body continues to metabolise insulin, so it looks like natural causes."
There were other clues that she was capable of killing those she was hired to care for. In 2008, in another state, she was at the centre of another potentially-deadly incident.
That incident took place in a Victorian medical centre as Haines was patrolling a ward on her own. It was reported that two women, on two separate occasions, were targeted by the nurse with "unnecessary doses" of insulin.
At the same time, in the same facility, jewellery was stolen from two patients while Haines was the only nurse on duty.
Haines had her registration suspended. On those occasions, it's believed financial gain was the motivating factor.
"So the patients just had these beautiful old diamond rings and things," a former colleague told Fairfax in Australia.
"And they were given insulin right at the end of the shift so they wouldn't be roused by the next person rostered on and find it missing."
In 2014, the motivation was something far more sinister. Revenge. Crown Prosecutor Brendan Campbell told the NSW Supreme Court during Haines' murder trial that the nurse had received a number of complaints during her brief stint at St Andrews in Ballina.
"Within that time she had accumulated a number of complaints from residents," he said.
Mr Campbell said Haines was addressed by former director of care at the centre, Wendy Turner, that three residents had made complaints about her. One was Marie Darragh, another was Isabella Spencer.
"The next morning, members of the jury, two of those residents that had complained were dead," Mr Campbell said in October.
During sentencing, Justice Peter Garling said Haines abused her position.
"Her conduct was deliberate and calculating. It was a gross breach of trust and flagrant abuse of her power.
"She clearly abused that position of trust. I consider this to be a significant aggravating factor."
Family members of Haines' victims said they were "over the moon" on Friday after learning of the sentence.
"You don't know when it's going to end, that's the trouble," Ms Spencer's brother Rodney Spencer said outside court.
"Or whatever sort of sentence she was going to get. But ... I'm very pleased with the sentence she got, you've got no idea."
Ms Darragh's daughter Jan Parkinson said she was "numb" but "happy that I'll never have to worry about her being out on the streets and doing this to anyone else again".
Haines will not be eligible for parole until 2041.
- with AAP
