A judge has rejected a Christchurch woman's claim that she shot and killed her neighbour's cocker spaniel with an air rifle because she believed it was attacking her cat.

Judge Michael Radford said he believed the woman's explanation in court was the one she wished she had given police at the time, the Court News website reports.

Yesterday he convicted Henrietta Tania Campbell, 47, on charges of wilfully ill-treating the dog and unlawfully firing an air rifle near a house.

Several animal protection campaigners wearing black Paw Justice T-shirts sat through the 90-minute hearing in Christchurch District Court.

Afterwards, the daughter of the couple who owned the dog, Althea Carbon, said it had been hard to sit in court and listen to Campbell's evidence, but the outcome was the best the family could have hoped for.

Campbell was remanded on bail for sentence on September 7 and the judge called for a report including suitability for home and community detention.

The police are asking for reparations of $520 to cover the veterinary bill.

The dog's owner, Alan Carbon, said the family pet sometimes escaped from their property in suburban Bryndwr, and they would always find it at a property along the road where friends had previously lived.

On January 12 he could not find the dog, but heard a popping noise and saw the dog come out of the driveway next door before collapsing bleeding in their drive. They took the dog to the veterinary surgery nearby but it was dead.

The autopsy showed it had been shot from behind or while turning away, with the pellet entering the chest, passing through the diaphragm and hitting a lung and the aorta. It died of blood loss.

Senior Detective Paul Johannson interviewed Campbell who told him: "I was just trying to scare it. I have had problems with other animals scaring my cat. I didn't mean to kill it. I'm sorry I did it. I was just sick of animals coming over here."

She said she had seen the dog on her property once before when it ate her cat's food. A few weeks before, her kittens had been killed by an unknown animal.

On the day, she said she heard her cat scream and saw the dog standing over it in the backyard. There was a handful of fur on the ground. She took the gun from the wardrobe and fired two shots out the window.

Defence counsel Serina Bailey said householders were allowed to shoot dogs on their properties if they were attacking stock or domestic animals. She said Campbell had a reasonable excuse for firing the shots.

But Judge Radford noted Campbell had shooed animals off on previous occasions but did not make a noise to try to scare the dog that day.

"I don't think for a moment she was trying to scare it away," he said. "I think the explanation she's come up with in court is the one she wishes she had given at the time. It is self-serving and I don't believe it."