The photo is directly on the glass, or is on paper fixed to the glass?
I'm wondering if it might have been a locket of some kind at one time.
Anyway, looking at the hair and the shoulder seam I would put this photo between 1889 and 1893. But, don't think that fashions would lag behind just because it's Australia, things weren't the same then as they are now...for one thing, all dressmaking was done by a local dressmaker, and the ladies' magazines, which were the authority on the latest styles, would arrive in a timely manner. Then, all that needed to be done was show a picture of the newest fashion to one's dressmaker, and in a week or so, voila! So, I'm fairly confident in the date window I've suggested.
Cheers,
China