An Australian woman faces 25 years in jail after she was arrested with 5.8 kilograms of cocaine at an airport in Colombia.

Cassandra Sainsbury, 22, was detained on April 11 at El Dorado International Airport in Bogota just as she was about to fly back to Australia after a working holiday.

According to the Daily Mail, The personal trainer from Adelaide was denied bail and is being held at the overcrowded El Buen Pastor women's prison until her hearing in two months, her family said.

Her older sister Khala was to pick her up from the airport on Easter Saturday and didn't realise Cassandra's predicament until the morning of Good Friday.

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The trip was at least in part to promote her personal training business, her sister told Daily Mail Australia.

The mother-of-four insisted her CFS volunteer sister was innocent and being "set up".

"Anyone that knows her, would say she is a kind, loving, happy kind of girl. She would help anyone out in need," she said.

"Our hearts break, because we know she is innocent, but stands little chance of proving it in such a corrupt country."

Her arrest came while Cassandra was planning a wedding next February to her fiance and "love of her life" Scott Broadbridge, 23.

They got engaged in October on a cruise to Vanuatu and New Caledonia and have dated for just over 18 months.

Khala said her sister was tricked into being a drug mule by a man she just met who handed her a package containing the concealed drugs.

She said Cassandra saw some headphones and decided to buy them as gifts for her bridal party and family friends, and a man who was showing her around said a friend could get them cheaper.

The cocaine was concealed in the packing of more than 15 headphones she was given the morning of her flight home.

"It came to her already packaged and concealed and she put it straight in her suitcase. She's very naive," Khala told 9 News.

The personal trainer (pictured with her fiance) was detained on April 11 at Bogota Airport just as she was about to fly back to Australia after a working holiday. Photo / Facebook
The personal trainer (pictured with her fiance) was detained on April 11 at Bogota Airport just as she was about to fly back to Australia after a working holiday. Photo / Facebook

Cassandra grew up on the Yorke Peninsula before moving to Adelaide.

"She has her full life ahead of her, and now its all put on the line because of this. We miss her so much, and since we have very little contact with her its very hard," her sister said.

Khala said her sister found a Colombian lawyer but he suggested pleading guilty to lesser charges to avoid an up to 25-year jail sentence.

"I'm devastated that my little girl is in this place. I'm scared to death for her. Our family just wants her home safe," her mother Lisa Evans said.

"I cant believe this has happened to an innocent young woman. Anyone who knows Cassie, knows she did not do this. It can happen to anyone," her grandmother Barbara Johns added.

The Australian Department of Foreign Affairs and Trade said it was providing assistance to an Australian woman arrested in Colombia in accordance with the Consular Services Charter.

"Due to our privacy obligations, we are unable to release further information," it said.