I have some different Idea for Tama. Maybe she is really related to Orochi and his clan. But my idea would be her family got saved by Oden or his father when the clan got stalked and attacked. Maybe they waved some of their kids and gave them a save place, which makes clear why she was living so hidden and far away.
that would mean, at the end of the story, Orochi would understand that he killed and poisoned the only leader in wano Kuni who tried to save his clan from the hate and attacks.
Sounds like a classic Oda to me.