"I just felt sick," she said. "How dare someone do that?"
She had bought the black and tan VMoto Milan JX50 partly so she could get to the course, which she saw as a possible new beginning after her life changed forever six years ago.
In 2006 Mrs Farren, then 30, was working as an architect in Ireland when she began having severe migraines. While waiting to see a specialist she become extremely ill and was rushed to hospital, where doctors found a rare golf ball-sized tumour in her brain.
She had surgery to remove it the next day, followed by six weeks of radiotherapy.
She was later told she was one of just 12 people her age worldwide who had undergone the same treatment - the rest had all died when the tumour returned.
While she has been lucky her tumour has not returned she does suffer from headaches and language difficulties, tires easily and has some memory problems.
On returning to Rotorua she worked part-time as an architect for three years but the constant headaches forced her to give up the career she loved in January 2011.
"It was too much, sitting there at a computer, I couldn't do it," he said. "I do miss it."
Since then she has been unable to find steady work, despite sending 65 flyers to prospective employers and calling each one of them.
For a while she turned her hand to art, exhibiting and teaching art classes at RAVE. But that wasn't enough to get by. "I've tried every single thing under the sun," she said. "Every job I apply for, [it's a] no." She's enjoying the arborist course and is considering looking for an apprenticeship once it's over.
But for the rest of the course she is back to walking and cycling.
"I'm telling you, this year has probably been the worst year of my life."
Mrs Farren knows it's unlikely she will see the scooter again, but she said if anyone out there knew where it was or had any information she would love them to contact the police.
"If it did come back I would be over the moon, I really would, but as the days go on you just think, nah, it's not going to."