Australia has a good and functional “safety net” for Australian residents and citizens. Australia has Medicare, the Pharmaceutical Benefits Scheme (PBS), and states like QLD (and I think VIC?) have free hospitals. However, if you don’t have health coverage for visitors from overseas who are Australian visa holders, it can be very expensive indeed.
Down Under Visa have long recommended strongly that all holders of Australian temporary visas should ensure they have adequate health coverage for their stays in Australia. That means to contact one of the private health insurers and organise overseas visitor health insurance for the applicant, because if she gets seriously ill then Medicare will not foot the bill. Don’t kid yourself! And do not assume that it will be cheap.