My TGF got an OZ visa last April without any problem. Applied online on her own (I helped her with the English). Yes, she had to do the bio-metrics and soon after, almost immediately the visa arrived.
Just for your info: Her daughter was in OZ at that time and my TGF works for the Thai Government, and received a letter from her office. If I remember right, it took less than a month.
I don't know why you would need an agent and the additional expenses. If she provides all the documents, that's it (how it worked for us).
Add
This was her first visit to OZ