Lying in a sweaty state, with slurred speech and opening her eyes only to painful stimuli, Heather Bills had just been injected with an almost unheard of volume of insulin, a medical expert told a court.

The 64-year-old died in Middlemore Hospital on January 2, 2013, six weeks after she was badly burned in an explosive house fire.

Her death has become the focus of a coroner's inquest over the next two weeks before chief coroner Judge Deborah Marshall in the Auckland District Court.

On the evening of November 22, 2012, she was pulled from the blaze after neighbours braved the inferno to rescue her from an upstairs room of her Orakei home in Auckland.

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She was then treated at the National Burns Centre and the intensive-care unit as her condition improved.

However, late on Boxing Day, 2012 her health quickly deteriorated as she developed low glucose levels.

She suffered a massive hypoglycaemia-related cerebral injury which resulted in an irreversible and fatal brain injury.

It became clear that her death had been a result of higher levels of insulin in her body and was suspicious.

In an email from Dr Brandon Orr-Walker to investigating officer Detective Senior Sergeant Ross Ellwood, the clinical head of endocrinology and diabetes at Middlemore Hospital said Bills was moaning and was thought to be in pain at midnight on December 27.

A coroner's inquest before chief coroner Judge Deborah Marshall will be held over the next two weeks. Photo / Michael Craig
A coroner's inquest before chief coroner Judge Deborah Marshall will be held over the next two weeks. Photo / Michael Craig

She was able to answer questions of the nursing staff, the email read.

"Forty minutes later a call bell was rung by the psychiatric watch. The patient was found to be tachycardic, sweaty, had slurred speech, and opened her eyes only to painful stimuli only."

Bills' condition only worsened as she "trembled, groaned and gasped to her death" over the next few days, her daughter Michelle Maher has said.

Dr Orr-Walker today respectfully disagreed with medical expert Dr Steven Miller about the quantity of insulin Bills had potentially been injected with.

"One cannot be precise of the timing or dosage of insulin," Dr Orr-Walker told the court.

He said there was no evidence of injection, but "there was little other physiological explanation".

"It's an incredibly unusual scenario," he said.

"This clearly was an overdose that was administered to her," Dr Orr-Walker said.

The court has heard that vials of insulin were being stored in drawers at the burns unit.

In his formal statement to the court, Dr Miller estimated that Bills had 666.67 units of insulin given to her by an unknown source.

It is an extremely high level, that only very rarely would be administered to a patient, he said.

"In such cases, the individual would be known to have diabetes with severe insulin resistance."

Dr Orr-Walker said that the dosage could have been higher or lower than Dr Miller's estimation.

He said a range of 400-1000 units was the likely dose.

Police have not ruled out reinvestigating three or more suspects based on the findings of the inquest, which continues tomorrow.