The 42-year old woman also suffered a gaping wound to her neck before she was rescued by her two sons and all three fled the house in Papatoetoe.
Her 69-year-old father-in-law Daya Nand was later found dead inside the house.
Police said today that no charges would be laid over the incident which was being referred to the coroner.
Detective Senior Sergeant Gary Lendrum said Mr Nand was pulled off the woman by her two sons, aged 21 and 17, and all three fled from the house.
She was transported to Auckland's Middlemore Hospital where she underwent emergency surgery to save her arm. She came out of surgery about 4am today.
Mr Lendrum said the dead man had a known history of causing problems within the family.
He said an argument broke out between Mr Nand and his daughter-in-law shortly before 10am yesterday. It is understood to have followed a request by the woman for her father-in-law to move out of the house because he had been causing trouble.
