And therein lies one of the enduring problems with this whole "nobility" concept of any society.
Gods forbid you're born a girl into a family / setting like that, because you're 100% fucked if you thought you'd ever get to have an independent desire or opinion or thought.
Makes for great (well, "easily writable") drama in story form like this, but it almost always just feels stupid. Doubly so with the adoption reveal, because that's even more "onus" on her to "be a parent-pleaser" and consign herself to a life of repression for "the sake of family and image and repayment".
I will say it really sounds like her own mother was giving her an out of sorts, going into that arranged marriage. If she truly spoke up, I hazard a guess that something could be worked out between her and her parents as far as her place going into adulthood within the larger company structure of things.
But of course, we can't have that, because she's a proper self-sacrificial lady who must shelve any hope of agency for the sake of doing what she thinks is expected of her based on "propriety", and I suspect it'll be up to the MC to step in and save her from her fate because she's a damsel who couldn't hope to do it herself.
I'd love to be wrong - but the MC and this story has very much been portrayed as that sort of deal, up to this point.