A young girl was attacked by a dog, leaving her with serious facial injuries requiring surgery, just a day after it was released from the pound following an attack on a teen.

Thanos had been classified as dangerous after the first attack, but was returned to his owner, Melissa Tuapawa, with conditions.

However, when the girl was playing fetch with Thanos in a garage the next day, he was neither muzzled nor on a lead, as required.

The circumstances surrounding the two attacks emerged when Tuapawa appeared for sentencing in the Wellington District Court this week.

The court heard Tuapawa had got Thanos as a puppy, but lived a chaotic and transitory life with the two sleeping in her car.

Despite this, the tan mixed-breed dog with black facial features was registered as a Staffordshire bull terrier and had been microchipped.

The first attack, in Wellington on January 21, left the 18-year-old victim, one of Tuapawa's relatives, with moderate injuries. He required Steri-Strips to close a wound to his face.

Before returning the dog, staff at the Porirua pound advised the Waipā District Council and Tuapawa, who was then living in Cambridge, that the dog was classified as dangerous.

Others in the house where Tuapawa was visiting were also told, but they and Tuapawa were adamant Thanos would not pose a risk.

But it was agreed no one should enter the garage where Thanos was being kept.

The council said it returned the dog because Tuapawa wanted him back and there was no prior history of aggression.

On January 31, Thanos attacked the girl, biting her face and causing serious injuries to her lip and cheek.

Tuapawa, who witnessed the attack, told the girl she was "sorry but was in shock".

The dog was put down two months later.

Girl still suffers nightmares

The mother's victim impact statement, which Judge Jan Kelly referenced during the hearing, described her agonising wait for the ambulance that took her daughter to Waikato Hospital.

The mother said her daughter remembered everything about the aftermath up to the point where she was put under general anaesthetic.

Her daughter spent three hours in surgery and five days in hospital, where her room had to be kept at 40°C to help her recovery. After her release from hospital, the girl required strong pain relief.

The mother said her daughter continued to suffer psychological harm from the attack, including distress over her significant facial scarring.

She also suffered nightmares, and her mother said the attack had significantly changed her personality.

The court heard at sentencing that Tuapawa was approaching seven months free of methamphetamine and had gone from being homeless and living in emergency accommodation to transitional housing and, finally, her own flat.

She was also studying towards a certificate in health and wellbeing.

Tuapawa's lawyer, Kevin Smith, said his client had pleaded guilty at the earliest opportunity to a charge of owning a dog that attacked a person, causing serious injury, and had written a letter of apology to the girl and her family.

Tuapawa's father had also written a letter to the court.

In it, he did not seek to excuse his daughter's actions, the judge said, but wanted the court to know about the changes she had made since the dog attack.

Judge Kelly noted that at the time of the attacks, Tuapawa was living a disorganised and chaotic lifestyle of which Thanos was a part.

Taking into account the aggravating factors, which included the victim's young age and the significant injuries she had suffered, as well as the fact that Thanos was not on a leash or muzzled, as required, Judge Kelly adopted a starting point of 12 months in jail.

Tuapawa's guilty plea and remorse were also acknowledged before the judge reduced the sentence to seven-and-a-half months' imprisonment.

Because the sentence was under two years, Tuapawa was eligible for a community-based sentence.

Having provided an address suitable for electronic monitoring, Tuapawa was sentenced to six months' community detention, which involved a nightly curfew.

It would be served alongside intensive supervision, which Tuapawa was already serving and would finish next year.

Judge Kelly declined to make an order for emotional harm reparation, saying Tuapawa could not afford it as she already had a large sum of outstanding fines.

Tuapawa would automatically be disqualified from owning a dog, but because Thanos had already been put down, no further orders were sought, the judge said.