Not much is known about C. Elizabeth Poppenborg, except that she was most likely of the Catholic faith. Records from St. Joseph's Cemetery indicate that she died in 1847, and was the daughter of Conrad Poppenborg and Lucy Burnan.
By doing a search on FamilySearch.org, I located a Maria Lucia "Lucy" Burmann. Maria's first husband was Casper Anton Ruenbusch Windau, who died in Germany in 1831. At some point Maria emigrated with her many children to the United States. She then married Conrad Poppenborg/Poppenburg, who worked on the Mad River Railroad.
Though C. Elizabeth Poppenborg is not listed in the family group on FamilySearch, I do believe she is a daughter of Conrad Poppenborg and Lucy, and she must have died quite young.
Thank you to my friend Joel M., for finding this treasured tombstone at St. Joseph's Cemetery in Sandusky, Ohio!