Tanta Hornblower Baggins
Hobbit of the Shire; wife to Largo Baggins. Tanta Hornblower married Largo Baggins and in 2864 of the Third Age they had a son named Fosco. Fosco became the father of Drogo, who became the father of Frodo. This makes Tanta the great-grandmother of Frodo.
Family Tree showing Balbo's relations to Bilbo and Frodo:
References
The Lord of the Rings, Appendix C: "Baggins genealogy," page 380
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