I personally would speak with a migration agent first to see what your chances are of getting a skilled independant visa given your trade. This gives you a whole lot more freedom and $200 up front with only a 'maybe' she can be included sounds a bit dubious although I apologise if I turn out to be completely wrong!!!
Good migration agents will give you a free assessment based on yours and your girlfriends situation i.e. living together etc along with the obvious - whether your trade, skills and experience is enough to get you the independant skilled visa.
You could potentially save a lot of money (or your girlfriend could) as international student fees are lots of $$$$
Try migration agents Go Matlida (sorry don't know web address but a quick google will sort it) or Ian Harrop & Assoc -
Registered Australian Migration Agents, UK - Ian Harrop and Associates who both come very highly recommended!