@Melissa ******
It's not hopeless. Your mom can still get a birth certificate at the Australian Embassy for you. It is important that she has the 13 digit identification number, id card or house registry. If you can find that out then it's easy. I went through the same thing. Call the Embassy. Explain your situation. Tell them why it is important for you to get Thai citizenship. They will be happy to help you. If you have any questions... you can send me a pm.