You will have to prove a long and commited relationship. Photos together, emails, amount of time spent together in Thailand and elsewhere. The Oz government has just announced a visa crackdown, so if you have only known her a short time you have no chance.
Many people absolutely hate Asia. Best you come and have a good look around before making any commitments. I love Bangkok but only in small doses. I prefer quiet beaches away from the pollution and the crowds. Every one has different wants and needs and different expectations. I will bet Thailand is nothing like you imagine it to be.