As far as I can tell, native and naturalized U.S. Citizens are not required to provide proof of citizenship on demand; but they can be required to prove citizenship when applying for a job or for government benefits. But ICE can't just raid the convent and carry away all the Irish nuns who can't provice proof of citizenship.

U.S. Citizenship and Immigration Services (USCIS) used to be the Immigration and Naturalization Service of the Department of Justice. They provide this page of information on how to apply for proof of citizenship:https://www.uscis.gov/us-citizenship/proof-us-citizenship-and-identification-when-applying-job

To get a replacement Certificate of Naturalization, she has to file form N-565 - and the filing fee is $555.

Back when I was a government investigator, I'd go to the U.S. District Court and review naturalization records myself, but I don't know if members of the general public were allowed to do that.

Guess I'll soon find out what I can do as a private citizen, now that I no longer have a badge.

-Joe-