Have your fiance check it in at the first airport and forget about it until Customs in OZ. The only airline Qantas can't get baggage from is Southwest (Qantas USA's website gives that info in the luggage section). The prority tags get your bags there everytime (even if you don't make a connection
. The last thing you need to do is go to a baggage claim and haul that bag down to Terminal 4 (unless that flight is out of TBI which is *much* worse).
We do that all the time and there's never been a problem. Though when you land in OZ, be prepared for a pretty intense customs routine that you don't see in North America/Europe. On a bad day (a grand convergence offour 747's landing in BNE at the same time) it's taken me more than 2 hours to get the bags (the hold is 'bug bombed' before the luggage removed) and go through immigration/customs.
OZ and NZ are very strict and run your bags through scanners looking for biological material and the food/drug sniffing dogs will make their rounds while you wait for the bags. I'm still feeling burned for Quarantine Australia emptying out the buckwheat hulls from my bucky neck pillow and handing me back the empty cover saying "At least you'll have the most important part!".
Hope you have a great trip!