Dear Ms. Peters,
Thank you for posting your request on History Hub!
If she became a naturalized U.S. Citizen, the National Archives will not have a copy of the certificate of citizenship. Certificates of citizenship were issued by the Federal courts until October 1991 when INS took over responsibility for naturalization proceedings. All INS records are now overseen by the US Citizenship and Immigration Services (USCIS). Beginning April 1, 1956, INS began filing all naturalization records in a subject’s Alien File (A-File). Certain A-Files may be requested through the USCIS Genealogy Program.
We hope this is helpful. Best of luck with your research!