Just get away from the psycho. If she's out on Saturday, go stay with a friend, take anything of value you have and put it in your car and go to a hotel if you have to.
I've dated women like this before and you just don't know what is truth, what is just talk, and what they will or won't do. You say she's been emitionally and physically abusive in the past, so just get away now and make this psycho part of your past right now.
Once she's gone, break all contact. Don't give her the time of day. Don't try any retribution to "get back" at her. Nut jobs like that will just view that as you wanting them back in the picture. Ignore them completely.
I'm willing to bet that anything she might tell the Austrailian Immigration beaurocacy will just be swallowed up in the black-hole of beaurocacy. If you really think that she might actually do that, contact them yourself and tell them you are planning to move there on the work study program and a jealous friend has threatened to mess it up. Get your side of the story to them first.
Good luck to you and remember these types thrive on conflict, don't give her any.
Anything worth having will take a great deal of effort!