Senua Oldblood
Importance:
Cailynn's mother, and the half of Cailynn that the Serpent's Grove recognises on sight. The creatures there name her as Senua's daughter and speak of her two bloodlines running together. Cailynn hears Talon and Senua in the voices and old memories of the place, and decides that the story she is in is her own rather than theirs.
Since then
The Grove remembers in both directions at once. Do not mistake that for forgiveness.