Hmmm not sure if the orange (was that the colour?) snake moving around actually confirmed it though. I think that snake appeared also when Shivanya was saving Hritik? So it couldn't have been here.
Instead, I think she was the brown-ish snake we saw on the trees last episode -- when Sesha was singing to lure in Hritik, there was a brown snake slithering on the trees following them.
As another poster said, I feel like shivanya is a nagin who acts according to what she thinks is right to do. She said that in her dialogue as well. It also makes me think like she's not a part of the whole revenge thing? But then, why would she be a nagin? Aren't nagins only given human form if they're given a boon from Shiv? Apparently that's why Sesha is a nagin? So Shivanya must've also been given a boon? Plus she seems to have a younger sister to care for. What's the story behind that? Was she adopted as a young girl or did she just randomly come across the little girl and make her, her sister? So many questions!
Shivanya's character is so intriguing and Mouni has done a really good job keeping her guarded!