Congratulations to you both!
You need to interview in the country you are a resident of, not holidaying in. So that will be Australia.
The only way you can do your interview in the US is if you were doing AOS - Adjustment of Status, and that's only for certain temporary working and resident visas, not holiday visas like the VWP (Visa Waiver Program - 3 month holiday visa that certain countries, like Oz, can use to holiday in the US).
Awkward timing but your interview could very well be in another month. If it does end up being in June, the only thing I can see you doing is changing your interview to a later date. However, there is a slight risk that visa numbers may run out.
With the large increase in OC selectees for DV2014, perhaps case-numbers will progress faster to account for the increase? If so, your interview might be sooner than June. You really can't tell until we get a few months of case-numbers out of the way, to see the progression. I have a spreadsheet of the past 10 years of OC case-numbers per month and it's so hard to tell anything. Using that, I could only guess that my interview would be sometime in January, February, March or April. It was in March but I could only tell that when they announced February cut-offs which I just missed by a handful. For 13xx, I see July and later being most popular months over the past 10 years but DV2014 is very different, so who knows?