Australian citizens are just that - citizens of a Commonwealth. We are not our Queen's subjects.

Queen Elizabeth II abolished any requirement to curtsy years ago, in all her realms. Although many/most women continue to do so some/many do not. It is relatively common in Australia for women not to curtsy. Whereas many years ago women would have curtsied to the Governor-General as well as to The Queen, even many women who would curtsy to The Queen would not now curtsy to the Governor-General.

As other people have observed, Crown Princess Mary would curtsy to Queen Elizabeth II as a courtesy.