It's a hefty sum, and if it can't be raised through online and community fundraising, Carley and Chris Jans will have to sell the family home - a home that is still being rebuilt after being gutted by fire two years ago.

However, that's a price they're willing to pay to ensure their eight-month-old daughter has a life free of prosthetic limbs and the associated pain and challenges.

"Sophia has a very rare limb deficiency called fibular hemimelia - there's only two other known cases in Australia," Mrs Jans said.

"It means she was born with no fibula in her right leg while her tibia is shortened, compared to her left leg, and her leg points down and she only has three toes.

"It's not genetic and we don't know why this happened, although we've been told she may have developed a blood clot as her legs were developing and budding."

Mrs Jans said the only treatment option in Australia was amputation, although the couple had found a doctor in Florida who could save Sophia's leg through limb reconstruction.

"Limb lengthening has been occurring in Australia since the 1980s, but the surgery also required to rectify the deformities to her ankle and foot is not available here," she said.

"It is not an option just to leave it due to that deformity, and the fact that as she grows, so will the length discrepancy between her legs."

The Jans - who have three older children - said the treatment by Dr Dror Paley had been successful for the other two Australian children with the same rare condition.

Dr Paley, of the Paley Advanced Limb Lengthening Institute, has confirmed that Sophia would be a good candidate for the treatment, which would include an initial nine-hour operation to correct the deformity and then three months of limb lengthening treatment in the United States.

Once back home, Sophia would have to wear an external fixator for three to six months before returning to the US for further treatment.

"It's a lengthy and expensive process, but it's our only chance to give her the best quality of life and allow her to keep both limbs," Mrs Jans said.

"Otherwise she will have to have the leg amputated and have to be constantly refitted for prosthetic legs as she grows, and deal with the complications such as pressure sores around the stump, chronic back problems and body image challenges."

Mrs Jans - a registered nurse who lectures at the University of Wollongong - and Chris, a firefighter, were devastated after the loss of twin boys at birth in 2009.

They were told any further pregnancies would be nearly impossible, so the arrival of Sophia in August last year was a godsend.

They have done everything to give Sophia - who was also born with talipes (club foot) to her left foot - every chance she deserves.

However, they are facing financial hardship after the 2013 house fire, and an associated battle with their insurer, and there is no Australian government assistance for the US operation.

Mrs Jans said they found it hard to ask for help, but were appreciative of the community support they had received so far.

Around $5500 has been raised online through the mycause page and a community appeal will be held on June 13 at the Novotel Northbeach.