When the woman -- named by the company as Mrs Wallis -- was admitted to the home in 2009, aged 81, she had disorders of the lungs, heart, thyroid gland and left hip.
In 2011, she suffered a cough, runny nose, diarrhoea, vomiting, weight loss and dehydration. On the 10th day of her illness, she was taken by ambulance to hospital, where she died three days later from congestive heart failure, dehydration, diarrhoea and heart-artery disease.
Ms Wall said the nurse failed in his duty to seek timely advice from a doctor when, on day six of the illness, the woman was not improving.
"Furthermore, on the evening of day nine, when [Mrs Wallis] had another episode of diarrhoea, medical advice was still not sought despite [a caregiver] clearly indicating her concerns to [the nurse].
"As a result, no medical assessment or diagnosis was obtained between day one and day 10 despite multiple entries in the records that [Mrs Wallis] was unwell."
This was a severe departure from accepted nursing standards.
The nurse told the investigation he had been mentored by the rest home's clinical services manager, a nurse, for three months, but she left and there were no plans to replace her.
He felt he was put under impossible pressure to maintain clinical safety in the company's two New Plymouth homes, Ms Wall said.
"He told HDC that he felt powerless and intimidated, and worried about losing his job.
"He said that he was consistently working over and above the call of duty, most often working 11-hour days, which was in effect the job of two registered nurses.
"Expecting [the nurse] to care for rest-home residents without clinical supervision was unreasonable and unsafe owing to his relative inexperience, and placed the residents and [the nurse] at risk."
Beta Pacifica, in a statement released by one of its directors, Paul Renwick, of Wellington, said the company apologised unreservedly to Mrs Wallis' family.
Internal and external audits had been done after her case and "monitoring structures were put in place to ensure that other residents and their families would not be put at risk in this way".