That dedication began in 1955 when she started teaching calisthenics to mothers of her gymnastics students who wanted exercise classes but had nowhere to go.
"I have to be honest, I don't think I deserve it - there are people more deserving of an award like this than me," she said.
After a few classes, word began to spread about the novel idea and she was asked by the YMCA in Devonport to teach more classes in a church hall.
"I think I was the only female fitness instructor on the Shore back then and when I held my first class more than 100 women showed up.
"We advertised it as a keep-fit class and all these women turned up. It was more calisthenics, aerobics were unheard of in those days."
Her approach was a novel one at a time when the only options for class fitness exercises were "either at the Y or Boystown" and often earned her strange looks.
"I think people thought I was a bit queer because of my attitude to fitness but having always been a sporting woman I knew the importance of fitness - and of course nowadays it's everywhere, isn't it?"
The great-grandmother specialises in senior movement classes at the North Shore YMCA five days a week, often helping stroke and heart attack victims referred to her by doctors and hospitals. She also teaches fitness classes at retirement villages.
Mrs Thornton, who trained as a physical education teacher, continues to seek new knowledge.
She recently attended the New Zealand Active Conference and a Heart Foundation training workshop.
She immersed herself in the YMCA - "particularly in the camping, coaching and gymnastics" - well before she was made a life member in 2005 and took pride in knowing that what she had done had helped people improve their quality of life.
"It's seeing the improvement in how you are helping them that is really nice but you have really got to love what you are doing," Mrs Thornton said.
"I didn't dream I would still be teaching at this age but I would like to teach until I'm 80."
