Where was the adoption done? Was she "readopted" or did her parents do a "registration of foriegn birth" in the state they resided?
WE, for example, readopted in WI, thus the State of WI has a birth certificate of record that my daughter can always obtain a copy of from the state's vital records office. NY allows a type of registration of a foreign birth for international adoptees. If that was done, a birth certificate copy would be available from Albany.
If the only birth certificate would be the adoption birth certificate, and that was done in Korea, you can write to the Korean Consulate and ask about the process of obtaining a copy of the one issued when the adoption was completed. My DH obtained a copy of his BC from a former Soviet Republic nation- faster than a record from NY!