I wonder if the sister left some kind of curse that remained on her through the regression (like how the family seem to have glimpses of the past loop) since she seems to be strangely negative when comparing herself to the sister.
She's aware she isn't talentless since the sister stole her power, so there's no need to think they'll treat her like a useless person.
It's not like there can only be one ward, so not sure why she expect to get kicked out as soon as the sister show up.
And in this chapter she learn about the pomegranate, which reveals the sister needed resistance spell, implying she wasn't given one.