The 13-year-old vividly remembers what her childhood friend, Grace, went through after being diagnosed with leukaemia when the girls were in kindergarten.

"[Grace] was a beautiful person, both inside and out, and she was always smiling and laughing, despite what she'd been living through," Siobhan, 13, said.

"I remember she came to school one day and we asked why she was bald; the shock of hearing that she was so ill and was receiving chemotherapy had us worried, but she stayed positive.

"She got the right treatment and in year 5 we really started noticing some change; less trips to the hospital, less medication and more hair on her head."

Her childhood friend remains an inspiration and is the driving force behind her World's Greatest Shave campaign this year.

She will join about a dozen of her Smith's Hill High schoolmates in having her head shaved completely for the Leukaemia Foundation campaign next month.

Siobhan will also donate her pristine waist-length locks to be made into wigs for chemotherapy patients.

After just three days of fund-raising, she had raised more than $300, and hopes to easily surpass her goal of $500 by the time her head is shaved on March 15.

To donate to Siobhan go to worldsgreatestshave.com and search for her name.

The World's Greatest Shave is on March 14-17.