Hi Maz & Jon
How ling is m-i-l planning to stay for? If 90 days or less, a 0--day ETA will suffice:
ETA (Visitor) (Subclass 976)
If she wants the flexibility to choose and to stay for anything up to six months, an e=676 is prolly the best bet:
Tourist Visa (Subclass 676)
Miles better to get the visa before she books the flights, though.
Best wishes
Gill