Well, is not really like that, because I went to Thailand with a 60 days tourist visa but my ticket out was the day 89, & it was accepted by the company desk because the extension. I think it will depend on the person, but from my experience it will be accept on a 90% of the cases. Just to he sure 100%, she can buy an onward ticket out before the 30 days, just 12$. It is also working. But is true that every company & every employee is different.
To go it won' be a problem because you have 30 days + 30 days extension once in Thailand, to return make the extension or pay 500 baths per extra day I suppose that Australians can get the 30 days extension as Europeans