Why had Natasha 2.0 introduced herself with the surname from her last life?
It was the name she went by, written in all her documents she got from Juno, after the imposter fled with her original body and identity.
If it went after Juno's plan years ago, she would have changed her name, as being in the same class with the same name and last name would be strange.
But if she had to wait years anyway, she wanted to at least keep her name from her last life. Juno also supported this decision.
Lance had hopefully forgotten about the imposter back then, and most possibly never knew about the imposter's last name.
She didn't have any ties in this life with the Pretsch family, but she didn't even remember her original surname before having been adopted by them.
Additionally, her little brother was meanwhile long dead.
So, when she saw a teenager with albinism, a boy at that, coming in the dining room, her pupils dilated.