I'm posting this question for my second cound.

She was born in a hospital in New York City in March 1980. She has a valid birth certificate issued by the State of New York.

Her parents were stationed in Washington, DC at the time, as military attaches of a foreign embassy.

She returned to the home country with her parents when she was 4 year old.

Recently she went to the local US consulate and applied for a US passport.
She presented all the necessary documents, including the NY-issued birth
certificate. However, she was advised that she's not eligible becuase children
born in the US to diplomats are not eligible for US citizenship. No further explanation was given.

Is there a specific US or internation law that covers this issue?

Thanks for any info!