Missy's owner, Mary Pehi, pleaded guilty in April this year to one charge under the Dog Control Act 1996 of being the owner of a dog that attacked another dog.
In May she was sentenced in the Waitakere District Court to pay reparation of $4580 to Wesley's owner and ordered to destroy Missy.
She appealed the destruction order in June but later added to her appeal, asking that she also be discharged without conviction.
Auckland Council said Pehi was seeking the discharge without conviction to get around the mandatory destruction order based on a previous judgement.
But High Court Justice Christine Gordon allowed the appeal to encompass the new request and to include an affidavit by Pehi, in the interests of justice.
In her affidavit Pehi said Wesley and his owner walked by initially without any problem on June 6 last year, though the Chihuahua had been "yapping" at Missy.
However the other dog owner let go of her lead causing Wesley to circle Pehi and Missy, she claimed.
This prompted Missy to take off after Wesley causing Pehi to let go of her dog's lead.
When the attack occurred Pehi sprang into action, grabbing her dog's lead and yelling at the other owner to do the same with her dog.
"She was just screaming with her hands over her eyes and I waved the lead in front of her face and she snapped out of her temporary paralysis and grabbed her dog's lead," Pehi wrote.
By that stage Pehi had yanked Wesley out of Missy's mouth.
The agreed summary of facts stated that Pehi threw Wesley at the complainant who caught the dog in her arms.
"The defendant then tried to throw a punch at the complainant, but missed and only made light contact.
"The defendant began shouting and swearing at the complainant saying 'pick up your dog' and calling her stupid. The complainant felt intimidated and was worried about Wesley so walked away."
Pehi said Missy, who as an American pit bull is classified as menacing under the Act and required to wear a muzzle in public, was not because a council ranger had threatened to prosecute Pehi if she put one on the dog.
But in her judgment issued on August 21, Justice Gordon said Pehi was told not to put a "tight nylon" muzzle on Missy and not to exercise her excessively when the muzzle is on because the dog would not be able to breathe properly.
"Ms Pehi should have used another muzzle."
Pehi's lawyer said the crux of the appeal to keep Missy alive was because she is the "best friend and guardian of Ms Pehi's 32-year-old son who has Down Syndrome".
Pehi said Missy plays a huge role in her son's life and her lawyer said the effects of losing his best friend would be nothing less than devastating for Pehi's son.
However, in the decision Gordon said there was no evidence to suggest Missy was a registered companion or therapy dog or a certified disability assist dog.
"In the end, every family whose dog is destroyed following a conviction is likely to suffer a sense of loss and grief."
She accepted Missy had never bitten a person or dog before but said Wesley's injuries were significant and the situation came about because Pehi lost control of her unmuzzled dog.
