I know I'm not a coach, but thought I would at least try and answer some of your questions. TOPs kids start at age 7(as far as testing) so most are compulosry in the beginning. The structure for the 7-9yos is based on strength and flexibility. After age 9 the emphasis is on learning higher level skills. TOPS is VERY specific on the way everything is done and the testing is tough. To get to national testing, your dd must be in the top percentage of girls from her state and then her region. Obviously learning all the things to be tested and getting them ready for testing takes extra hours in the gym and more money from you. Testing typically is done in the summer for each state. There have been mulitple threads on here regarding the benefit(or not) of doing the TOPs program. Some gyms love it and others don't. The USAG site has alot more info on exactly what is required and how the testing works. It could easily take your dd until next summer to be ready to test, so I imagine the coaches are looking at the test for a girl over age 9. Does the gym have a TOPs group? If so, stop by and watch their practices.
As for the competing in Australia---don't really get that one. The systems are different so levels don't transfer exactly and why take a young girl there(not saying anything bad about Australia---I would love to visit!!!)? There are many many nice invitationals in the US where she could go to get her feet wet in doing larger meets in front of judges from across the country.