"She fought long and hard but unfortunately, the condition was too aggressive, ruthless and relentless," he posted at the time.
"Thanks to her treatment, we don't believe she suffered any pain during her fight and was able to leave this world peacefully."
Family friend Sarah Watton set up a GoFundMe page to help the family. Since its launch, the site has raised more than A$32,000 ($36,000).
"I know there are no words to comfort Ruby's mum & dad right now as they try their best to navigate through this incredibly tough time so I was hoping to try & help them financially," she wrote.
"Any donations, no matter how large or small, would be greatly appreciated; if you aren't in a position to donate, could you please share this with your family & friends."