I was also curious as to the MC's difference in reaction between Fleta and her sister. But then it's revealed that she did eventually come to know that it was her sister who masterminded the abuse on Fleta. Not sure if she ever did anything to stop it though since the scene ends there, I suppose we'll have to wait if it's further explained later on. I suppose there's a sense of hypocrisy along those lines, but I think she blames herself just as much for not doing enough for Freta prior to her regression, hence why she's being overprotective and overly attentive (to which developed genuine affection towards her).
Also, her sister harasses her from time to time so their relationship was never at the best of terms.

MC is really ignorant and just a dumb hypocrite ( ̄∇ ̄")
The first chapter was bomb ngl very refreshing, but then after regression, it's became cliché. I can't connect with the MC or any other characters, I don't feel any of their emotions. The author is trying so hard to paint her older sister as villainous but in the first chapter her personality was very different. She was just trying to kill the monster who destroyed her family but the MC started disliking her for that? Her self righteous act while being so powerless is annoying. She is the same as everyone. A bystander who lead fleta to turn into the monster she became.
The plot is now very predictable hence it makes the story really boring. The forced romance is just... ew.
little fleta is the only likeable character so far maybe cause she is just drawn so cutely