Obtaining Duplicate Taiwanese Birth Certificates

Greetings, all. I am a US citizen, living in the US. My fiancee was born in Taiwan, and currently has dual Taiwanese-Belizean citizenship. We are about to get married, and will be filing for her Green Card so she can start towards obtaining US citizenship.

We have one snag, however: my fiancee does not have her birth certificate. Her parents do not have it, either.

Can anyone direct us as to how we can go about getting a certified copy of her birth certificate? Can it be procured over the internet?

Any help would be greatly appreciated. Thanks much.