If she wants to go to a drama college then it doesn't really matter which country she's in, does it?
As for the HSC, I think its difficulty is relative to the student's academic drive and their intellect, and I assume that's the same for A levels. In hindsight, I found the HSC easy, because it is when compared with university. But that's not going to be everyone's experience: I know some who were having daily panic attacks over the HSC, and one of my best friends got so badly burnt out that she's never wanted to further her education since.
The university matters to an extent, but not as much as it does in places like the US. Most unis in Australia are decent. Some get their reputation purely from their name, and not from the quality of their education. I looked at going to Sydney Uni when I was first starting out but hated it at the open day: the snobbery of it was out of this world. UNSW had a much better vibe, but specialises in Engineering, so that's a consideration. I ended up at Macquarie, which specialises in Business, and I got a double degree in Business & Law. I was happy with that choice and have not had any difficulty getting good jobs since.
The ATAR requirement is a bit of a crock, honestly. The ATAR requirement for Law at the time that I got in was something like 96, but I had people in my course who'd gotten in with ATARs in the early 80s, ditto my friend who was at UOW had people in her course who'd received ATARs more than ten points below the minimum cut-off. It depends on the popularity and demand for the course as to how willing they are to let people in who don't meet the requirements.