If she enters with an Australian passport, then she's Australian to the Thai government and will have to deal with visas, extensions, and other immigration matters. Why would she even consider this? Get her a Thai passport and then she doesn't have to worry about anything.
fill out this form from the owner of this Facebook group. It will ask you for some details about how long you've been in Thailand and such. Then it'll give you a price for guaranteed entry st the airport.