Then, the weekend before her big day, Sapphire was running a high temperature, so her mum Jasmine Parsell decided to take her to the emergency department at Wagga Base Hospital, where blood was taken for testing.

Sapphire returned home with her mum, but when the results of those blood tests came back, they showed not a minor illness, but acute lymphoblastic leukaemia through 90 per cent of her blood.

"It was a huge shock. Sapphire's never really even been sick before," Ms Parsell said.

Instead of celebrating her third birthday on April 2, Sapphire was flown to Sydney and given her first dose of chemotherapy.

Her treatment schedule is expected to last for two years.

Ms Parsell said the first year will involve more intensive treatment, with additional testing and chemotherapy likely in the second year.

Sapphire's condition is further complicated because her leukaemia has spread to her brain and spinal fluid, which happens in only about five per cent of patients, and means she has to have six weeks of daily cranial radiation treatment.

Ms Parsell is in her second year of her social work studies, but has put her education on hold as she needs to spend huge amounts of time in Sydney while Sapphire undergoes treatment.

Even when Sapphire is home from Sydney on breaks between treatments, her compromised immune system means she cannot attend daycare, or even do something as simple as play with friends at the playground.

Just running a temperature means Sapphire is likely to need hospitalisation and treatment with antibiotics to ward off any potential infections.

Sapphire's illness has come as a second blow to her family.

Her younger sister Hazel, 21 months, has childhood epilepsy, which has seen her hospitalised frequently in recent months.

Hazel has a chromosomal disorder and it is hoped she will eventually outgrow the seizures.

For now, Hazel is facing long periods of separation from her mother and sister, when Sapphire is in Sydney for treatment. Hazel often remains in Wagga with her grandparents.

In a bid to help out the family while Sapphire's treatment continues, friends of Ms Parsell have set up a fundraising page and in four days have helped to raise $5537 of a $7000 goal.