You will need to do the application through the Home Affairs website. Register an immi account and complete the application.
Use the same information from previous successful applications. Even if you think it's not necessary, upload as many documents as you can to support her application. Particularly bank statements, chanotes, and other income such as work or business.
Because your wife has visited in the past and returned, it will help to support her application. After you have submitted the application, you will be asked to provide biometrics. Even if you have done this in the past, it's still required. Follow the instructions and make an online booking with VFS Global. This will allow her to use the smart gates when entering and departing.
When I did my wife's application last July the approval time was 4 months, however, it was approved in 5 weeks. So keep that in mind before booking tickets.