"The heartbreaking story behind my favourite 'unicorn' dress."

And not just because it’s an incredible ‘unicorn’ dress – mythical, legendary – because it hasn’t faded in colour in five years of being washed with my son’s dirty socks, and doesn’t need ironing, and has only lost two sequins. A dress that I could wear to a wedding, the beach, or to do the groceries, and it would look perfect.

A dress that I’ve worn on Christmas Day, and also to my father’s funeral; five kilos heavier, five kilos lighter.

I bought the dress from a little business called Carey and Carey in my hometown of Adelaide.

That's really where the magic of the dress began.

One sunshiney day, I saw a fellow school mum wearing a darker version of the dress, glistening at pick up time from across the car park, and knew I had to have it. So on another sunshiney day very soon after, I made my way to the location of Carey and Carey. It turned out to be a house belonging to Tania Carey, who owned Carey and Carey with her twin sister, Tracey.

I don't remember the details of meeting the twins, because I really was focused on the dress. But I do recall the general impression of them being effortlessly glamorous and beautiful.

I could never have known what was really happening in their lives at that time. It wouldn't be until a few years later when our paths crossed again that Tania and I became friends, and I would learn that the dress was very special to her too.

Tania and Tracey had been inseparable since they were born. So when I ask Tania to give me a special memory of their bond, she finds it challenging to narrow down, but eventually tells me of a moment in her sister's wedding to husband, Chris Diamond.

"I was Tracey’s Maid of Honour, I held her hand in the church briefly, a moment I will never forget. The ceremony was in Greek so we did not understand it, she reached for my hand part way through, I think for comfort. It was a fleeting moment but one that has stuck with me ever since. When you marry a twin you get the twin sister as a part of the deal, I was ever present in their life."

Shortly after she married, Tracey fell pregnant. It was an exciting time, but Tracey was very unwell and experiencing severe and prolonged episodes of diarrhoea.

"At the time it was believed to be her body’s response to the pregnancy," Tania says. Tracey listened to her body, and underwent a colonoscopy, which dealt a devastating blow: she had advanced rectal cancer.

As Tania explains, "She was fit and healthy at the time of her diagnosis, and was an avid runner, netball player and horse rider. She was 37 years old."

Tracey bravely faced a lengthy and painful journey in her fight to get well.

"The first of many procedures was surgery for a colostomy. Tracey then had chemotherapy, followed by an elective caesarean at 32 weeks pregnant, to deliver their angel Harlow."

It was an immensely difficult time for the family, but Tania was grateful that she was able to be there because "caring for her and Harlow was a full time commitment."

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Tania recalls the arduous, roller-coaster of a time that lay ahead for her sister; "In the months following Harlow’s birth, Tracey completed courses of chemotherapy and radiotherapy, and in September 2010 had surgery to remove the tumour in her bowel. At this stage she thought she had beaten bowel cancer, but as it turned out it was just the beginning."

A scan showed that the cancer had spread to her liver, and it later spread to her lungs. Tracey never gave up, and endured many rounds of treatment and surgery, "believing all the way somehow by way of miracle she could beat it."

It was at this point that Tania decided to start the fashion name Carey and Carey, enlisting her sister's input whenever she was well enough.

"I was driven by a need to show Tracey I was still moving forward and although she was very sick I thought it might be something she could help me with," Tania says.

Tracey fought a long, hard battle, but the cancer was determined and aggressive. She passed away in February 2014.

Her daughter, Harlow, was just four at the time.

When Tania first told me the history of Carey and Carey - that it was borne of a sister's love - I understood why there was something special I could sense about one of the last items they ever sold - my beautiful unicorn dress.

When Tracey passed away, Tania knew her "heart just was not in it anymore. The company was called Carey and Carey for a reason not just because it sounded good."

Totally devastated by the loss of her sister, Tania joined forces with the Jodi Lee Foundation to raise money and awareness about bowel cancer, which is often a silent killer. Tania ran the New York Marathon for the foundation, but also spoke around the country to thousands of people, bravely detailing her loss so that she could help save lives.

Everything Tania has done for the cause has been in her  sister's full married name, Tracey Lee Diamond, so that it truly is her legacy.

Tania is certain that Tracey’s story could have been different if her cancer had been detected earlier. She advises that if you're worried about changes in your bowel movements, you shouldn't stop investigating the issue until you have an answer.

When asked how Tracey would feel about her tireless work, Tania predicts a typical sister response, "I think she might hate all the fuss that I have created if I’m honest!"

But Tracey would undoubtedly be immensely proud, and know she was incredibly loved.

Because it's their love that I feel every time I wear my magical unicorn dress.