It is fairly common now unless you are married that your Thai girlfriend will be asked to go for a body check if you apply for a tourist visa to Australia for 6 months to 12 months. We always advise applying for a 3 months tourist visa to Australia first and then something longer so if you do apply for a 6 month to 12 months then be prepared after you put in the visa application to Australia for your partner to be asked to go for a body check.

You should not go for the medical yourself before you are asked by the Australian Embassy because each medical has a unique number added to it which should be given by the hospital.

Always consider using professional services when applying for an Australian tourist or settlement visa