The grisly injury happened last December when the Pokeno teen went to investigate the washing machine, which had opened mid-cycle after the mosquito net had become knotted.
Her father, Peter Bennett, had been alerted to loud noises coming from the washing machine in the moments leading up to Hannah's ill-fated decision to reach into it.
"The machine didn't register the door was open, I could hear it, 'Bang, bang, bang' from the shed," he said. "I saw Hannah crouch down. I ran, yelling 'Don't put your hand ... ' - but it was too late."
The power of the still-running washing machine was so great that the remaining tendon was spun around four times.
With their daughter in shock, the Bennett family drove on the wrong side of roads to Pukekohe's accident and emergency clinic. She was stabilised and rushed to Middlemore Hospital. She spent the next two weeks in the burns unit where specialist hand surgeon Dr Bruce Peat - and 120 leeches - worked to save her thumb.
After two operations, leeches, a native variety harvested by farmers in Northland and Waikato, coaxed blood through her arteries and veins while her tendon realigned.
"The leeches would get couriered to us, each was worth $30," Hannah said. "We nicknamed them. A few were quite naughty, they went wandering. I woke up one morning and said 'There's something on my back'. Mum didn't believe me. A phlebotomist [a blood test collector] visited for my daily blood test and when it was over I could still feel something on my back. I turned over and yup, there was [the leech], wriggling around."
Nine months after the incident, Hannah is left with a 14cm zigzagging scar on her right wrist.
During exams, the Year 12 Pukekohe High School student has been coping with 40 per cent sensation in her thumb and must dictate exam answers to a transcriber.
Peat told the Herald on Sunday that he has repaired digits torn off by people involved in activities such as water skiing and rodeo riding, but had never seen a washing machine injury before Hannah's case.
The messy tearing of Bennett's thumb meant "she probably had a 50/50 chance of saving it," Peat said.
"The vessels I was repairing on that thumb are only 1-2mm, if they get stressed and traumatised it's really difficult to repair them."
