The stoush came about over a small area of jointly-owned land on which Mr Ellis planned to lay a driveway and had constructed a retaining wall.
During a hearing at Auckland District Court Tuesday, police prosecutor Fiona Culliney said Mr Ellis considered he had authority to build on the Waiheke land while Ms Ross considered he did not.
She said the case was not about who had rights to the land but about the charge of intentional damage against the defendant.
While giving evidence on Tuesday, Ross said the former rugby star-turned-TV personality had refused to engage with her over the bitter dispute regarding his driveway.
"If he'd had the courtesy to talk to me... and go through the due process we might not be here today," she said.
"I feel he must take responsibility for his arrogant attitude."
Mr Ellis, who also spoke, said he was taken aback when he saw a photo of the alleged damage taken at the time.
"It's worse than I remember."
He is one of five trustees who owns the property on Alan Murray Lane.
They had planning permission to build a house and a driveway, which was put in so work vehicles had access to the site, he said.
Mr Ellis did not make an appearance at the sentencing.
Speaking to the Herald after the verdict was handed down, Ross said she was "amazed and shocked" she was found guilty.
"I am disappointed obviously. It wasn't the outcome that any of us expected," she said. "I am going to meet with my lawyers and discuss possible options and then go from there I guess."