This whole thing feels like a typical subpar or amateur Web (or Light, idk the original source's medium) Novel writer moment: focusing too much on getting the plot moving that you end up flubbing the plot/character's coherency and/or steep it too heavily in (poorly implemented to outright eyerolling) tropes. I'm confused as to what the hell made Kiara suddenly complacent - she went from going straight to a wounded victim who will likely die despite knowing it would arouse several questions, to wasting two weeks about "what to do" to prevent the manga's events transpiring? There's being cautious, and there's simply doing nothing, doubly so for someone who was initially a medical worker with experiences under tight pressures.
She didn't even need to be proactive about the "peaceful" annulment thing (which, really, is a simple "Richard I know you like my step-sisters and not me, so let's just swap the roles now"), wouldn't building up rapport with the father and some of the other servants suffice? She already mentioned that the thing that kickstarted the OG FMC's melodramatic turnovers was her father dying, which she prevented. I dunno about it completely fixing everything, but there would at least be some level of pushback during this whole outburst from Richard by the dad and every other servant calling out how bullshit the lies are from how she's been behaving amicably and dutifully.
I dunno, the more I think about this, the more weary I am of the following chapters' writing quality. At least the art is still on point, mostly.