I totally had the same thought as soon as that line was said.
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.
They are implying that Viviana got her body taken over by her mother, because her mother was obsessed with power and youth.
Tffff that's news to me or actually, I think I forgot that minor detail being mentioned
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