She was seen immediately and transferred to the intensive care unit, where she died the following morning.
Chris Lynch Media previously reported the patient died from sepsis, but was initially sent to the waiting room after being triaged by a nurse, and collapsed some time after this.
Sepsis is the body's extreme response to an infection.
The leaked email stated that the patient had been triaged appropriately and this was a system failure rather than an instance of workers failing to perform their duties properly.
A Health NZ spokesperson said the email was sent to clarify the facts for ED staff, who had been upset by some media coverage of the death.
"Te Whatu Ora Waitaha Canterbury acknowledges that Christchurch Hospital's ED needs more clinical staff – we are in the throes of recruiting significantly more staff for ED with a specific targeted campaign about to start," the spokesperson said.
"Most of our services are carrying significant vacancies due to the fact it's a global market for talented health professionals and there are worldwide shortages."
Richard French, chief medical officer Te Whatu Ora Waitaha Canterbury, acknowledged the ED was busy during this period, which meant wait times were longer than usual.
French said 71.7 per cent of patients who turned up to Christchurch Hospital's ED were treated within six hours.
"This is lower than we would like and is due to a number of factors, including multiple trauma incidents occurring, acutely unwell people presenting to ED, staff shortages due to illness and vacancies, and the flow-on effect to the ED as our primary care and urgent care facilities are also under pressure," French said.
He claimed that 374 people had come to the emergency room on the day the woman arrived and that since then the number has fluctuated between 322 and 374 per day.
"We have excellent specialised and experienced nurses, doctors and allied health professionals working in our ED. Our staff are working extremely hard in challenging circumstances, and we greatly appreciate the commitment and compassion they show every day," French said.