This does not have the 3 black submarginal forewing marks that characterise M. signifera. Also M. signifera is a tropical species. I think this is more likely M. amorpha.
OK, looking at this again I think you are likely to be correct. But I also note that the ALA records G .Cocking collected M. signifera as far south as Bermagui - well south of Canberra albeit on the coast of course. These species are quite variable it seems, but I overlooked M. amorpha because the first specimen that showed up on the ALA page looked very different. . However there are darker specimens on the ALA of M. amorpha which are a very good match for this sighting.
Maliattha amorpha and signifera are similar and both are variable. They are difficult to distinguish in live photos - set specimens in the ANIC collection show M. amorpha to be browner overall, and and to more consistently have a dark streak extending from the central dark band across the forewing up to the apex. Most ANIC specimens of both species are from north of the Qld-NSW border, and those from NSW and ACT are M. amorpha.