Police said they had launched an investigation into Folole Muliaga's death, which happened within two hours after state-owned company Mercury Energy cut power to her house Tuesday.
Mercury Energy's general manager, James Moulder, said the company was devastated by the woman's death and was conducting its own investigation to determine what happened.
Muliaga, a schoolteacher with four children between the ages of 5 and 20, had been off work since February with an illness and had fallen behind in her payments to Mercury, said Brenden Sheehan, a relative who provided a copy of the bill.
Six days before a Mercury Energy representative arrived Tuesday at the house to disconnect the electricity, she was $122 in arrears.
Brenden Sheehan, the woman's nephew in-law, said both Muliaga and her son told the technician she was dependent on the oxygen machine to stay alive and invited him into the house to see it.
Muliaga's son, Letitaia, said the technician told them he was "doing his job, he's here to cut the power off."
Sheehan described Mercury Energy's actions as "reprehensible."
"It's absolutely disgusting what they've done," he said.
Muliaga began having difficulty breathing, became faint and then collapsed, he said. Paramedics were unable to revive her, and she was pronounced dead within two hours of the power being cut.
Moulder expressed his "deep condolences" to the family, and said the company was checking reports that it had been warned Muliaga needed power for the oxygen machine.
"We were simply unaware that loss of electricity to the household was putting a vulnerable customer at risk," he said.
"More than one" disconnection notice had been sent to Muliaga's address over a six- to seven-week period, he added.
State Owned Enterprises Minister Trevor Mallard said there were reports the family had been warned about the overdue account.