The story of Túrin Turambar goes back to the end of the First World War, and Tolkien continued to work on it through the 1950s. Later versions repeatedly describe Túrin’s sister Niënor figuratively—as or like—a hunted deer, especially after her enchantment by the dragon Glaurung. Tolkien identified Sigurd the Volsung, Oedipus, and the Finnish Kullervo as sources for Túrin, however, the motif of a maiden enchanted as a deer does not derive from those sources. The Irish story of Oisín’s mother, Sadhbh or Saav, who was transformed into a fawn by an evil druid, shares several analogous narrative elements with the later Niënor passages. Thus, the paper concludes that Niënor can be read through the motif of the Celtic deer-woman, and that the Saav story serves well as a “hard analogue” in this regard.
"The Deer-Maid Motif in The Children of Húrin,"
Journal of Tolkien Research: Vol. 17:
2, Article 5.
Available at: https://scholar.valpo.edu/journaloftolkienresearch/vol17/iss2/5