When Allison Lang learned her three-year-old half-sister in Canada needed a new liver, she offered hers without a second thought.
"Anyone would do anything to save their family," the 21-year-old Aucklander said.
At the start of the year, just after Ashlyn Lang's third birthday, the toddler was diagnosed with Tyrosinemia Type 1 disease following her mother's determination to find out what was wrong with her.
Ashlyn, from Kelowna in British Columbia, was born with redness in her hands and a swollen stomach which doctors put down to a "baby belly", said her mother, Lisa Lang.
And as the little girl grew, she developed bowed legs and rickets.
"We just got brushed off time and time again," Lisa Lang. "She was just so miserable and never slept so I finally turned into a crazy mum in the hospital and demanded that they do some testing on her.
"It took eight or nine days before they diagnosed her with her disease and then everything kind of made sense."
Ashlyn's belly was swollen because her liver, kidney and spleen were enlarged due to her liver being unable to break down a protein.
And her legs were bowed because her body was starving and eating her bones. "Basically all the protein that she eats turns to poison in her body," Lisa Lang said.
The cirrhosis of her liver destroyed the organ beyond repair and greatly increased her chances of developing liver cancer.
Ashlyn's only option was a liver transplant.
"We put the word out and instantly Alli came back and asked, 'What can I do? Can I be a donor?"'
The Aucklander turned out to be a 100 per cent match and so flew to Edmonton, Alberta, last month.
Allison and Ashlyn share father Corrie - a Canadian who came to New Zealand in the 1980s to play softball.
The two siblings know each other well from Allison's regular visits.
In 10 days, Allison is scheduled to donate part of her liver to her younger sister.
Once completed, it's then a waiting game to see whether Ashlyn's new liver takes and that the rest of her organs bounce back to normal.
"But we're all hoping that she'll be a very healthy little girl," Mr Lang said.
Doctors have told Allison that it will take about two weeks for her liver to grow back to its normal size, but it will take up to a year before life will get completely back to normal.
She'll also have to take annual liver function tests to ensure everything is working as it should.
But Allison's not that worried about the repercussions from her part in the surgery.
"I think with any type of surgery there's always nerves that start to creep in, but like I've said to my family, because I'm so focused on the effect that it's going to have on Ashlyn - I'm looking forward to her getting stronger and her improving - that it's sort of taken a lot of the nerves and the stress away.
"It's just something that needs to be done for her to improve," she told the Herald on the phone from British Columbia.
"In my eyes I think I've got the easy end of the stick with the whole process."
Allison, an aircraftwoman in the Royal NZ Air Force, played down her role in saving Ashlyn from a life of pain and hospitals, saying it's something anyone would do for a family.
However, her stepmother was bubbling over with praise and gratitude for Allison and her courage.
"It's a beautiful, beautiful gift that she's giving her sister - we're just so fortunate," Lisa Lang said. "Alli's just so brave. She's 21 years old and is just amazing. She has no reservations whatsoever and she's just ready to go. She's so wonderful."