I have searched the WA Vital Records Online Db (I am in the USA) to exhaustion. I've read, however, that in many cases of actual orphans, migrant children, and early child protection services when the church stepped in they often changed names, dates of birth and in some cases did not register births at all - only maybe recording christenings and making THOSE records untouchable.
There are no female children - on record - born in the state of Western Australia for the 4 year period I've searched in the past under ANY spelling of the family name or even under first names of known parents with no surname listed. Aaarrrgghhh!
We are now down to this possibility.