I hope that she and her sister manage to have a good relationship at the end of this. Soleil doesn't seem like a bad person.
I hate when villainess stories make the "original heroine" character just "the real villainess (but secret)". Unfortunately, that's even
more common in stories where the villainess is getting revenge.
Is it too much to ask that the villainess gets to find some happiness with the people around her? Maybe come to an understanding and caring relationship with good people who were only enemies by circumstance?
Apparently there's an audience for villainesses girlbossing their way into being the Supreme World Empress Who Gets All the Revenge/Men, but I'm personally mostly here for the potential the genre has for redemption arcs. I wish more authors would realize the two aren't necessarily mutually exclusive, if they really want the former.
Now, there is something that gives me a bit of hope: she spared their father at Soleil's request. She needs to protect Soleil from their father right now (and tell Soleil how their father treated her if she doesn't know), if Soleil is going to be on her side. If Soleil is just going to be an "original heroine pretending to care for Selene but actually the big bad evil behind the scenes" trope, I'm going to drop this instantly. I would much rather Selene behaves as a real head of the family and cares for Soleil as part of the family she is now leading.