I have helped my Thai partner to apply for a few Australian visas over the years. The procedure is a little tedious, however you do not need an agent. Firstly, your friend must create an Immi account. After that, there’s the online application. She should probably apply for a VISITOR (subclass 600) visa. The process will include submitting the usual Passport scan, Thai ID, payslips, employment letter, bank statements, credit card details, etc. After submitting the online application, she will receive an e-mail with instructions to attend an authorised facility to submit biometric data (fingerprints and face/retina scan). There may also be follow up e-mails, requesting additional scanned documents. Again, the process is not difficult (especially with your help), but very tedious. Note that it is important to make no mistakes in the application. Below are a few links to help get started. Good luck.
PS - I forgot to mention, your friend should login to her Immi account frequently, to check the application status and for further information/scan requests (occasionally e-mails can get lost).
*************************************
*************************************************************
********************************************************************