if your daughter automatically became a U.S. citizen through you and already has a U.S. passport, she is a citizen.

The passport proves citizenship, but a Certificate of Citizenship is an even stronger, more permanent document. (Passports expire; certificates don’t.)

You must file Form N-600 Application for Certificate of Citizenship this is the official application to get her citizenship certificate.

You, as the parent, file it for her because she is still under 18 you are allowed to apply for her directly.