An inspector arrived at Harrison's Wainuiomata property, where the 11-year-old gelding was tethered about 20m down a bank part way along a winding gravel driveway.
His broken halter was tethered around several trees, leaving him about 1.5m of space to move, Judge Butler said.
The gelding, named Zorro, had no grass or viable feed around him, and had two empty plastic containers nearby. There was also no faeces in the area.
Harrison had provided two containers of water to the horse shortly before the inspector arrived, and Zorro had consumed them immediately.
He was emaciated and had suffered a wound on his right hind leg.
The inspector tried to lead Zorro back up the bank, but after only a few steps the horse fell back down the bank. He was unable to be led out of the area due to his weak state.
After consultation with a vet, Zorro was euthanised to mitigate his suffering, Judge Butler said.
Harrison told investigators she tethered Zorro in the trees about three or four weeks earlier because he would not stop chewing through an electric fence cable and fleeing onto the road.
She could not remember exactly when she tethered him there, but said he was in an "okay condition" at that time. She recalled bringing him water once but could not remember if she gave him water any other time.
She did not provide him any food in that time because she did not have the money to feed him.
Harrison also admitted knowing Zorro's leg had become injured when he slipped down the bank, but didn't know when it had happened.
A veterinary opinion stated if Zorro was in fact in a good condition when first tethered, he would have had to have been provided with no food or water the entire time he was tethered.
The hilly environment prevented him from moving around freely, and Zorro would have suffered "significant unnecessary distress" from hunger, pain, loneliness, and inability to move anywhere.
Judge Butler said Harrison was going through "significant personal issues" at the time of the offending, and said she told investigators "I just thought he was okay".
She did not ask anyone for help with Zorro, and though she did call the SPCA in October 2019 to ask if she could surrender the horse, nobody returned her call.
A witness saw the horse while driving past one day, and in January messaged Harrison asking what was going on.
Harrison told the witness Zorro was being used as a weekend playmate for children.
Another witness asked for permission for his daughter to go feed Zorro, but permission was not given because the horse was unwell, Judge Butler said.
Defence lawyer Zachary Meehan today argued Harrison should be discharged without conviction, saying she had worked for 20 years in a field that requires criminal background checks.
He said her personal circumstances were relevant "to provide some context as to how what started out as a well-intentioned endeavour obviously ended up in such tragic circumstances".
He described Harrison as someone who had been a "pro social member of the community" for her whole life.
But the SPCA prosecutor said this was a situation where Harrison had possession of an animal that was "entirely reliant" on her to provide the basic necessities of life.
"It was a complete failure to provide those necessities," she said. Harrison had "knowingly" not provided the basic requirements to the horse.
Judge Butler declined the discharge without conviction application, as well as an application for permanent name suppression.
He disqualified her from owning animals for 10 years and ordered her to pay vet costs and court-related costs.
Harrison sobbed into her hands in the dock as her sentence was handed down.
