It is always advised that after your Thai partner has been to Australia on a 3 months holiday visa and enjoyed their time that they should reside back in Australia for a period of 1 month before applying again for another holiday visa to Australia. If you are planning on something more permanent like a settlement visa to Australia or a Fiancee visa to Australia then you can start the process immediately on your partners return to Thailand.
If you are planning on another holiday 3 months or 6 months then reside back in Thailand for one month and then apply. There is no written rule but this is our advice because if you do not give it breathing space before your next visa application to Australia they can use the excuse to refuse that you are using tourist/holiday visas to Australia to reside with your Australian partner which holiday visas are not designed for.
So to be safe give it some breathing space before re applying for an Australian tourist visa.