Naganeka's Venom?

So in the Twilight of the Gods story, we see a serpent-like Ascendant by the name of Naganeka, who, from her description, sounds extremely similar to Cassiopeia. Now I'm wondering just what the relationship between the two is, and how this affects Cassiopeia's character. Are we to assume that it was Naganeka's venom in the snake statue that guarded the Tomb of the Emperors? If so, why did the transformation even occur in the first place? In the story, it's stated that Naganeka's venom blinded her life-bearers, so why were they blinded, while Cassiopeia was transformed and gained powers? Doesn't that seem counter-productive if the whole point of the serpent statue was guarding the tomb?