A former nurse has been jailed for at least 27 years for murdering two residents at a northern NSW aged-care facility by injecting them with lethal doses of insulin.

Megan Haines, 49, was found to have murdered Marie Darragh, 82, and Isabella Spencer, 77, in May 2014 at Ballina’s St Andrews Village, after learning they had made complaints about her.

In the NSW Supreme Court on Friday, Justice Peter Garling described the murders as “particularly serious”, noting the vulnerability of the victims and the registered nurse’s significant breach of trust.

Haines had previously been suspended after complaints about her in Victoria and had only recently started work at Ballina while she was subject to reporting conditions.

The judge said Ms Darragh had complained about Haines refusing to give her a cream to soothe an itch, while Ms Spencer said she had refused to help her reach the toilet.

Hours after learning of the complaints, Haines went into the medication room between midnight and 1am, removed two syringes, drew up two injections of insulin, and administered them to the women, probably as they slept.

In jailing her for a maximum of 36 years, the judge described her offences as “deliberate and calculating”, and a flagrant abuse of her power.

Outside court, Ms Spencer’s brother Donald said he was “over the moon” about the sentence.

“I knew I would lose my sister sooner or later, but not in those circumstances,” he said.