Dear Ms. Ford,
Thank you for posting your request on History Hub!
We suggest that you request a certification of non-existence of a record of naturalization from USCIS (Genealogy Frequently Asked Questions - see About Further Research section), as well as submit an Index Search request to the USCIS Genealogy Program. USCIS should be able identify any naturalization records that exist for your great-grandmother.
We hope this is helpful. Best of luck with your family research!