It was in 2011 that Mrs Matthews began to feel unwell.
"The doctor kept saying I had a virus. But doing my swimming you get a good sense of your body."
Early in 2012, she noticed a lump on her neck. She told a nurse, who urged Mrs Matthews to immediately see a doctor.
"I thought, this is ridiculous."
But then she noticed a "huge lump" on her jaw. The former Chanel College principal was diagnosed with cancer in July 2012.
She was put on a waiting list for treatment, and in the meantime the lumps kept growing.
"Fed up" with waiting, she turned up at Wairarapa Hospital.
"The nurse took one look at me and got me an appointment straight away, and this kicked off a lot of medical procedures."
By this time, Mrs Matthews had two lumps on her neck and the one on her face.
A lump was removed, luckily without causing nerve damage, and Mrs Matthews said it seemed like "forever" waiting for the results.
Mrs Matthews' husband, Les Morris, was away working in Wellington when she received the phone call from the doctor.
"He said, 'It's not going to kill you, but it will never go away - it will probably just keep reoccurring and we'll have to manage it every time it does.'"
Mrs Matthews recalls aimlessly pacing around her garden digesting the news.
It was decided the most suitable way to treat her would be with radiation therapy.
This involved having a tight mask over her face, which attached to a bed that sent radiation through holes in the mask.
Because she suffers from claustrophobia, Mrs Matthews had to be given sedation and a panic button during each 15-minute session.
After doing this every day for five weeks the lumps went down.
"I thought, yay, I'm okay. These things do come back but I thought that won't happen to me."
Mrs Matthews began entering swimming competitions around the country, paying the entry fees and booking flights, cars and accommodation. But at her six-week check-up more lumps were found, this time on the lower half of her body.
She was told she had "stage three", which was "quite advanced cancer", and chemotherapy was necessary or else she could die. The chemotherapy made her feel "like a sick zombie".
"I used to spend time walking around the garden, even at night, because I couldn't sleep properly. It's really horrible stuff they put into you."
She said there would be 10 days of feeling "absolutely crap" after the treatment, but as soon as she started to feel better her next appointment would roll around and the cycle would start again.
She had chemotherapy from December 2012 until May 2013.
During this time she kept her sense of humour alive by writing about her experience in a "comic" Facebook blog.
Once her treatment ended she promptly returned to her swimming club and, within a month, had set herself the goal of competing in the world swimming championships in Russia.
In her three specialist butterfly events, Mrs Matthews came away with a bronze medal in the 100m and two fourth places, competing in the 60-64 year age group.
"I was so pleased to have got what I got ... I was 100th of a second away from second place - I was so chuffed I didn't care."
Mrs Matthews said having experienced cancer she now "frets less over the small things".
"It gives you a better perspective of life. It makes you enjoy things and appreciate things more - you stop taking things for granted. There's nothing more important than health because if you don't have health, you don't have anything."
