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They are, and they mentioned stuff along the lines of "they are used to having her and pampering her, so that won't change" except yuan was so jealous of mc that she tried to create incidents and blame everything on her, creating the gap now. Of course, the family is so stupid to believe yuan. So now they are facing the result of their actions
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Imma be fr, but I don't understand the "she's young!" card used in this context. And I don't think the family raised her to be this kind of brat, but they did show favoritism to her and she knows this. Before the fl was even there, they were all over her(yuan said this herself, so it's confirmed.) I fully blame her for being this shtty, cuz imagine seeing the real daughter come back, and then immediately getting threatened cuz she's prettier than you. She always had that greed in her, and she knew how to use the family's favoritism just to make the mc's life miserable. I would've agreed if from the very beginning the family always knew they were switched, and we're trying to desperately find the "real daughter" and she felt threatened cuz of how much they focused trying to find the mc. If that happened, I would've agreed with you, but unfortunately Yuan is just a lil greedy btch who got everything handed to her.
from what i remember, the little sister is actually the daughter of the maid/nanny that got fired. i forgot what she did yes shes evil(pretty sure she attempted murder on the mc), but the parents are the worst. they toss her aside now, and theyre basically repeating their actions towards the mc. like imagine being a kid not knowing whats right or wrong, then being tossed by the people who raised you terribly. i dont rlly blame her for how she feels, bec of how the parents raised her, her actions reflect the parents. is it so hard to just treat them equally? idk ultimately, i just hate all the adults in the story.