^Maybe it changes from state to state, but about 12 months ago I landed in Brisbane and drove off in a car from Avis on a 1 month rent with only my Thai licence. No problems at all. My Thai Missus could have driven the car too, I asked for insurance policy reasons.
But there's no way in 5 hundred fucking years would I ever let her loose in a car like that (Caprice with a 6 liter V8) surrounded by people who value their lives, and expect those around them to have at least basic road awareness. Driving around Pattaya in her little Jap shopping trolley, no problem. In Oz with road rules that actually apply and consequences for those who break them, in a large powerful car, no way.