Find out first if you do get married in Australia, if that marriage will be recognised when you apply for a spouse visa at the US Consulate there. If not, I highly suggest you get married in the US to avoid complications. True that her family won't be there, bt in life there are certain sacrifices we have to do. Sometimes we have to take a step back to move two steps forward.

I had to endure this when I married my Polish wife in the US. We had a small civil ceremony and her family was not there, mostly just common friends and my family. 3 years later (later this year actually), we are getting married again in a catholic church in Poland, and this time her family will all be there.

You can go this route too if you want. But the bottomline is ther are certain rules you have to go around of in order to get your end result. Sometimes the best route is not the shortest one.