She was born with neutropenia, where her body doesn't make neutrophils, a white blood cell vital that fights infection and creates a healthy immune system.

The initial treatment included regular injections, but about five years ago it stopped working as well, and now doesn't work at all.

Friend Sally Rose McShane, who is helping support Lauren's fight, said the condition is quite rare - and when the injections stopped working, the medical team decided a bone marrow transplant was the best form of treatment.

"They were hoping that would fix the condition," Ms McShane said.

"She had to do chemotherapy, to totally wipe out whatever was left of her immune system whatsoever, so she had to take immunosuppressants, chemotherapy for a few weeks, it was horrific.

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"No matter how bad she says it was, it was worse - it was the most horrible thing to see someone go through, having no immune system for a few weeks your body just shuts down and she couldn't even eat, it was just horrible.

"Worst experience of her life - but the whole time she was going through this she was positive, saying it was going to work, that she was going to have a normal life."

But it didn't work.

Just before Christmas, Lauren discovered that her body had rejected the bone marrow transplant.

"It was absolutely devastating," Ms McShane said.

"For them to suggest that she's going to do it again, she has to go back into that knowing it probably isn't going to work, going through how horrific that is."

Ms McShane said there are approximately 38 million people on the bone marrow registry worldwide.

In Australia, there are around 170,000.

Despite this - Lauren has just two matches on the registry worldwide. One wasn't viable - the other match is the person from the first transplant.

It's a challenge to find the perfect bone marrow match - because genetic markers need to match, including ethnic backgrounds.

That's why Lauren and Sally are now urging anyone aged between 18 and 35 to donate blood and register to donate bone marrow.

"She's a very strong woman and hates a sob story, hates people feeling sorry for her, but she also realises that's what's going to get people on the registry now," Ms McShane said.

"There's a really small chance you'll actually get called up to donate bone marrow, and the blood you're donating can help so many other people.

"If you're not her miracle, you might be someone else's."

Lauren is due for her bone marrow transplant from the previous donor in May - and while the likelihood of finding another match is slim, there's still hope.

"If it doesn't work, she dies - that's the blunt thing, this is her last chance," Ms McShane said.

"She wants to live, she wants to be able to party with her friends and go to work, she wants to have a normal life and she's going to keep fighting for that until she has no other option."

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