Biblical Reference/ Fall from Grace/ Expulsion from the Garden of Eden?

I really like your interpretation - it's extremely thought-provoking. It hadn't occurred to me to think of the literal meaning of Appleyard. Many things fit - Mrs. Appleyard stands for conventional authority and morality, of which conventional religion is part of. The whole thing fits a William Blake-like (particularly in The Marriage of Heaven and Hell) view of falling from the grace of traditional religion and conventional morality as necessary to assert oneself. Miranda is in fact a literal temptress, at least for Sara - she's explicitly compared to an angel, but then again Lucifer was an angel. Also, this is done in reference to Botticelli's Birth of Venus - which does not depict an angel at all, but a pagan goddess in the nude (in rather stark contrast to how everyone is overdressed in the Australian heat), so there is an element of subversion of conventional religion and dress. The girls, save for Edith, do not come back, just as those expelled from Eden cannot go back. Just as Adam and Eve disobeyed the injunction not to eat the fruit of the Tree of Knowledge, the girls disobey the injunction not to explore (i.e. in some sense seek knowledge of) the Rock, which had been described as "tomboy foolishness" - they explore in defiance not just of orders, but also in defiance of traditional gender roles. The Rock itself was also sacred grounds for the pagan Aboriginals, so again there's a subversion of conventional religion. Of course, the injunction not to leave the picnic area can also be read as "do not stray from the path."