Ahh..... a student aged 20 having her voice trained. .... well if I look back at my family histories ... one of my parents and their cousins were aged in their 20s in the 1930s .... and were all involved as students at the "Sydney Con" .... So although a different era to your lass, I see nothing odd about being a student involved in Classical training ... voice or instrument ....
In NSW again, I can assure you, that many of the NSW Deputy Registrars were part timers... for example some were also selling postage stamps, confectioners .... some were Clerks of Petty Sessions at local court houses ...
I don't have intimate knowledge on Vic BDM but if it were NSW , then in the tiny townships of the post gold rush goldfields districts the Deputy Registrars were ... (in my opinion) .... often almost illiterate, inexperienced with ink and pen, and sloppy in their recording. They were not given much support by NSW Reg Generals Office and were often multitasking.
NSW Registrations .... Births were driven by the family attending, deaths were driven by the funeral directors, and marriages were driven by clergy. So births were registered by informants without a huge experience portfolio to follow, whereas deaths and marriages the process would have involved experienced people on both sides of the counter. Pro forma documentation was not introduced until post WWI in NSW.
I wonder if a similar set if practices operated in Victoria in the years up to the end of WWI.
JM