Oh? I thought it's foreshadowing about Vivian mom. And the one who got vessel stolen was her mom that's why she died at birth. And I think that's why her teacher took her in since Vivian was a child. Or else I couldn't see why they even bother to mention her mom in this story. It's so insignificant.
She "died" under mysterious circumstances and she also acts completely different to how original Viviana was supposed to be, that and including the fact that she keeps stealing mana and holy power. Iirc there was also a mention of soul transfer magic that the mum was researching, but not fully sure if I remember that correctly.

Calling it now.(づ ̄ ³ ̄)づ