Dear Ms. Comlin,
Thank you for posting your question on History Hub!
There are a few pieces of basic information you will need prior to searching for a naturalization record. These include the city where the naturalization took place, approximate year, name at time of naturalization (account for marriages, name changes, etc.). Compiling as much of this information as possible prior to conducting a search is helpful.
We suggest that you review NARA’s "Resources for Genealogists" page: https://www.archives.gov/research/genealogy/start-research/nara-resources , as well as the History Hub Blog titled Suggestions and Advice for Family History Researchers. Also, the FamilySearch Research wiki for United States Genealogy may be useful.
Vital records, such as birth, marriage and death records are usually held at the state or county level. You may wish to note any name variants or broaden your search for the surrounding years. In addition, the FamilySearch Research wiki for [How to Find United States Vital Records] may be helpful.
Information about census records can be found on our website at https://www.archives.gov/research/genealogy/census/about. Many of these records have been digitized and are available through our partners. For additional information about accessing these records, you can visit our website. You may wish to search Ancestry or FamilySearch for the U.S. Census. There may be a fee for using Ancestry. Instead, please check for access at your local library as many library systems subscribe to these sites, making them free for their patrons.
If she was the person married to Henry Geis in Brockton MA, she would have been naturalized through her husband when he was naturalized and would not have separate naturalization records. According the the censuses in 1900 he is listed as an alien, but in 1910 and 1920 he is listed as a citizen (NA = naturalized). In 1920 it states he was naturalized in 1908.