yet aurora's plans (if she had them, following your reasoning) lead to karina being considered a liability to get rid off.
taking the position of crown princess from her sister was a harmful act because karina's rights were stripped from her.
and the whole staff of servants took it as an invitation to openly humiliate and neglect her, to curry favor the new crown princess.
the difference in treatment is undeniable.
karina had secured her own position in a power structure and was crushed to be replaced.
her sister's speculated intentions matter less in comparison to the results their relationship developed to.
you'll have to point out to me where all the staff and servants openly humiliated and neglected her. I saw nothing indicating that, and even in the castle she was exiled to in the north, the few servants we see, including the main one Karina most interacted with, gave no impression she was even willfully disobedient, let alone hostile toward Karina.
And, their parents also don't seem to hate Karina, or treat one favorably over the other. They treat Aurora as the sickly child she is in the flashbacks, but they don't ignore or abuse Karina; they hold her in high esteem and have great expectations for her, but they don't just demean and deride her.
If anything, Karina's skewed perspective of everyone around her is making
her perceive them as hostile. Thus far, the
only individual who, independently of her actual viewpoint, actually wants to hurt/remove her is Orlando the Prince.
Aurora, in all of the flashback we see of them as children, seems to look up to Karina, with bright smiles and eyes, and speaks nothing but words of praise and admiration toward her older sister. I'd argue even her giving the stuffed animal back, was an honest attempt to "make up" with Karina, as Karina was forced to give it to Aurora by their mother back when she'd first received it.
And I was actually reading back through to try and verify your hostile servants claim, and I'm now of the opinion that Aurora has had a mostly-passive role in all of this, as far as Karina's engagement annulment and exile.
Orlando wanted Aurora since the engagement was first decided upon when they were children; Karina was put forward instead by their parents because of Aurora's health issues. Karina stepped up and did her best, but Orlando barely paid attention to her - and while it's not yet been explained, I could see it being the case that--once Aurora grew a bit and perhaps got over some of her health issues--Orlando thought "well now she's healthy enough to become Queen" and
he cast Karina aside, and took Aurora via his own (Crown-backed) selfish whims.
But Aurora
did dissuade Orlando from sending more troops to "finish what the assassins started", and instead sent a bevy of maids and additional decorations/furniture to that castle, turning it from a "darkened and dreary place to one of light and comfort", to paraphrase Karina herself. (Yes, Karina saw it as her sister defiling her last-remaining home and thought of it as an act of mockery, but that's Karina's skewed perspective in all of this.)
Aurora could have been lied to about the machinations against Karina, or she may have thought it was for the best if Karina was tied to Orlando. We don't have confirmation at this point, though I suspect we might get
something next chapter, now that she and Karina are face-to-face for the first time in years. We also don't see (at least as yet) what she thinks in the interim, when Karina is presumed dead and her name is scrubbed from the histories by the Crown. But that doesn't mean that she either orchestrated this result, or that even if she tried to help Karina in some fashion at certain points, that she could have foreseen the outcome - especially if she never accounted for Karina's distorted view of their relationship and of Aurora as a person.
In effect, all of the animosity between Aurora and Karina is seemingly all on Karina's end. Aurora is frail and merely engaged to the First Prince, who openly detests Karina. Aurora might not be scheming or making big moves to either dethrone/exile Karina,
or to save/protect her, but she's done a few small things that allude to their happier childhood together, seemingly unaware of how Karina would react - and all of them would be within her direct power to do, as opposed to sweeping edicts or unilateral power moves that are beyond her reach.
That is to say - I don't think Aurora's oblivious in all of this; I don't think she's an antagonist toward Karina in reality, and that Karina is blinded/has an otherwise heavily distorted view on who her sister is. Aurora isn't spinning webs of schemes, but looking at this chapter - she wasn't surprised to see Karina, which I think means she didn't believe her sister was dead all this time. But she doesn't look angry to see her, either - and this is on her wedding day/a big step in her becoming Queen.
I did say that I think that maybe Aurora had something to do with the annulment of the engagement - looking through everything again, I would amend that to "she didn't fight against the annulment", and I don't think she had malicious intent toward Karina in light of it happening. But to your original statement of her being at best oblivious, I do think she's more "powerless" in the face of the First Prince to actually help Karina in any quantifiable way, and definitely not in a way that Karina won't misinterpret as malice.