Looking at Rosetta's pov there's 2 possibilities that comes to mind
1) What Riftan feels does not matter. Max has already married him. There's nothing more to say about Riftan especially when he has no relation to the sister (in upbringing and blood). Especially with the social setting, it seems like the general expectation is for the woman to stick with her husband no matter what.
2) Rosetta's mind is already set that Riftan is like all men (aka her father). So if her mind is already set, why would she bother confirming if Riftan might be different or not.
You bring up good reasons, but if anything, that only makes me question the author's intent even more. I can absolutely see why Rosetta herself wouldn't bother questioning Riftan. If she's already convinced that men are fundamentally the same and that women are expected to endure whatever comes with marriage, then from her perspective, there's probably nothing left to discuss. What confuses me is why the narrative chooses to have Rosetta cast doubt on *Maxi's* feelings instead. The reader already knows the lengths Maxi is willing to go to for Riftan. We've spent the entire story watching her worry about him, sacrifice for him, and shape major decisions around him. Her devotion isn't really the thing being questioned, nor should it be, especially with what I know about the subsequent arc after the end of Book 1. During the first half of Book 2, Maxi spends a significant portion of the story trying to reach Riftan, understand him, and get him to communicate with her, while he's the one who repeatedly shuts her out and emotionally stonewalls her.
So now, the question to my original point shifts: Rather than having Rosetta question the legitimacy of Riftan's devotion herself, I think the more interesting direction would've been for her conversation to make MAXI question it. Instead of doubting her own feelings, Maxi could've started asking herself whether Riftan truly loves her for who she is or whether he's in love with an idealized version of her. That would've felt far more meaningful to me because it directly addresses one of the biggest issues in their relationship while also giving Maxi something new to reflect on.
So, I don't necessarily dislike Rosetta, but I can't honestly say I like her all that much either, mostly because, as someone who's read the novel, it feels like the author never really knew what she wanted to do with her. Which is a shame because Rosetta had the potential to be one of the more compelling characters in the story. A lot of what Rosetta tells Maxi isn't even wrong. Her cynical views on men and relationships make perfect sense when you consider her upbringing, and some of her observations about Maxi's relationship with Riftan aren't exactly baseless either. What bothers me, though, is that the narrative seems more interested in having Rosetta question Maxi's love for Riftan rather than Riftan's love for Maxi. And that's where I get confused.
Rosetta is positioned as a character who sees through illusions and questions relationships, but I feel the narrative has her questioning the wrong person. Why would Rosetta doubt Maxi's devotion when the reader already knows how Maxi feels about Riftan? We're in Maxi's head for most of the story. We see her constantly worrying about Riftan, risking herself for him, and making major life decisions with him in mind. She followed a noblewoman she hardly even knew into a war zone because she was terrified something might happen to her husband. She dedicated herself to learning magic partly because she wanted to be useful and stand beside him as an equal. Whether those motivations are healthy is another discussion entirely, but her feelings for him are never really in question.
So why isn't Rosetta questioning Maxi about *Riftan* instead?
Considering her views on men, it would've made far more sense for her to be skeptical of *his* devotion instead of Maxi's. Why not ask whether what he feels is actually love, or whether he's simply obsessed with an idealized version of Maxi? Why not challenge the way he constantly tries to control her while insisting it's for her own good? That feels like a much more natural direction for Rosetta's character than repeatedly questioning feelings the reader already knows are there.
That's part of why Rosetta feels like she's a confusing character to me, especially after her return in Book 2. She had the perfect perspective to challenge some of the story's assumptions about love and romance, but the narrative never really lets her push on the questions that would've been the most interesting.