she's clearly insanely traumatised and has experienced what seems to be severe parental abuse, she fights with her life at stake on a daily basis only to be met with scorn by her citizens, has lived her whole life believing she's incapable of being loved (and the one lady who did seem to care for her that we know of is gone), most likely has ptsd judging by the painful memories and her reaction to them. in this very chapter she has to put on a literal mask of coldness and anger to hide her moment of weakness as a coping mechanism
Oh hell yeah, severe PTSD, and not just from the constant fighting of monsters and so forth, or even from the (apparent) childhood of neglect and abuse, but also I'm guessing that she ended up killing her father because otherwise he would have killed her - the perfect nightmare-flavoured sauce to go on top of the pudding that's been simmering in delicious trauma juice for twenty-odd years. Yum.
the pushback to someone who outwardly seems extremely suspicious (and literally does have ulterior motives) is completely understandable from her pov if you keep all these things in mind, not to mention the marriage was forced on her, and her territory she's been fighting tooth and nail for is at stake. all her general brashness and bluntness makes sense when you keep in mind she's had almost zero human interaction whatsoever, seemingly trash parenting and the fact that main fl is literally the only person in her life who doesn't fear or outright loathe her. she's one of the most believable tsunderes of all time i dont get your take
Clarice kind of had ulterior motives at the start, but she's almost forgotten them by this point - and not just because getting at Frost's supposed riches to help her family is clearly taking a back seat to making sure she doesn't get her head chopped off by the Black Knight, she's also just ended up totally focused on this new (albeit really weird) life, and on Frost herself. That focus started out as it's own form of trauma response, given how their married life started, but I do think it's progressed beyond that to something a bit healthier (though it's hardly anything you might describe as a healthy relationship, of course).
But Frost is absolutely acting like a raging prick. Not that she can help it, of course - that's one of the things that severe trauma will often do to people. But the fact there are entirely understandable reasons for it doesn't change the nature of her behaviour towards Clarice: she's being a total prick towards someone who's really only ever shown a generally positive and supporting attitude in a difficult situation.
Getting Frost to recognise that she's been behaving really badly is probably going to take up a lot of this story. And it'll be a difficult task, since there's so much deep-seated trauma here . . . but Clarice didn't really have any idea
why Frost was behaving this way until now - she didn't even really understand that there was trauma involved at all, though she's not an idiot so I'm sure she had an inkling that
something was going on. Now, though, Clarice is going to see just about everything Frost does through that lens, and (since she's a genuinely empathetic and caring person) almost every interaction they have is going to be coloured by Clarice's empathy and care rather than by the tinge of fear that's been underlying everything previously. And that's going to just make Frost
so uncomfortable and freaked out . . . which will be expressed as defensive anger, of course, but which Clarice will be much better equipped to deal with now that she has a better understanding of what's underneath it.
Though it's definitely not going to be plain sailing - Frost's violent actions are probably going to end up escalating as things progress. Not targeted directly at Clarice, since I think they're well past the point where there's any risk of summary execution, but things like the desk beng smashed up and walls broken and so forth will probably happen more often, and particularly in response to Clarice expressing care and empathy towards Frost. And while Frost is clearly capable of very precise violence that damages exactly what she wants to damage and nothing else, the more she feels uncomfortable and freaked out by Clarice's caring responses, the more likely she is to lose that precise control - I can see Clarice being hurt accidentally by one of those outbursts of anger.
That sort of thing is often used as a way to progress a story, with the sudden realisation of what they've done breaking through the traumatised and violent character's defenses . . . but I really hope that's not how this goes, Clarice deserves better . . .