A slightly better photo of the brooch from the Age
Below is a colour photo of the Princess with the Koala. Despite this photo suggesting that the Princess' brooch might contain aquamarines, I am still trying to evaluate if the brooch could be the gift brooch pinned horizontally. From the Australian Women's Weekly http://trove.nla.gov.au/newspaper/article/47509832/4940763
And a black and white photo from the same occasion.
According to the Age the Princess wore the brooch on her arrival in Melbourne but the photos are not sufficiently clear to identify it.