The severity of her injuries confirmed police's decision to enter the house immediately.
Two officers drew their weapons and approached the house while a third officer waited outside with the sister.
Both officers called out for Hemopo to show himself, but he remained in a bedroom and yelled out: "Get f***ed.''
The officers then forced open the bedroom door to find Hemopo clutching a knife, with his pregnant partner crouching beneath him.
Fearing he would stab his partner, the officers opened fire simultaneously with a Taser and a Glock pistol.
Hemopo received a gunshot wound to the back and fell to the ground, dropping his knife.
The officers handcuffed him, snapped off the Taser wires and carried out first aid until an ambulance arrived.
Hemopo, also known as Duane Thomas Makatea, survived the gunshot wound. He remains in custody on charges relating to the incident.
IPCA chair Judge Sir David Carruthers said the whole incident, from the time police said they were entering the property to the time shots were fired, took about one minute.
He said police were justified in shooting Hemopo.
"The police officers involved faced a complex, high-pressured and quickly-evolving situation. Despite this, they followed policy in all respects,'' Sir David said.
The IPCA also released its findings today on a fatal police pursuit in Hamilton earlier this year.
Rocky Joe Kohatu Hepi, 17, was killed when the stolen Nissan Maxima he was driving crashed into a stone retaining wall on Baverstock Rd, Nawton.
A 14-year-old boy in the front passenger seat suffered serious injuries, while a 15-year-old girl passenger suffered minor injuries.
The IPCA found police did not breach its policies relating to pursuits.
Police gave chase after they noticed the stolen car driving with its lights off along Rotokauri Rd about 1.48am on February 6.
Suspecting the driver was drunk, the officer signalled for the car to stop. However, it accelerated away and began to drive erratically due to its speed.
The officer pursued the car for 43 seconds, along 1.1km of road, before abandoning the chase due to the Nissan's unsafe driving.
As the officer drove slowly over a rise, he saw the stolen car lose control and crash into the wall at the corner of Baverstock Rd and Wexford Rise.
Sir David found the officer complied with police's fleeing drover policy, including its policy on speed and the manner of driving. The officer did not exceed 90km/h during the pursuit.
"It was a tragic incident caused by the actions of Mr Hepi that resulted in his death and caused serious injury to one of his two passengers,'' Sir David commented.
"In this instance the authority has not found any breach of police policy however, the authority is continuing its discussions with police about a general review of policies connected with the pursuit of fleeing drivers.''