But most of Merrin's observations and interpretations of them are still - at the implicit level difficult to verbalize, let alone put numbers on, let alone link up into a coherent logical case for why he should listen to her and do something differently.
Laeirthe is surprisingly unhelpful on the matter, probably because he has fun but he doesn't need fun to be functioning at his best, he just needs there to be a problem left to solve, and that character trait came through a lot stronger in the version-in-Merrin's-head than the original canon.
Anyway. Merrin hasn't, at this point, even gotten close to considering if she should, like, have a conversation about it? There is a point at which it would solidly feel like she was making a mistake, on an interpersonal-relationship-ethics level, by having her concerns silently and not telling him. But that point isn't now, mostly because it feels like if she tries the conversation will be full of culture-gap pits full of metaphorical spikes and she'll probably end up communicating some different concept that isn't actually what she meant, and that does not sound like a way to decrease Estha's stress levels at all.
(Trusting him might? He did say something that hinted that he maybe wanted her to trust him more, but - one, "trust Estha" is not an atomic action Merrin can just decide to take, trust in someone is a belief-state and that's not how beliefs work, and two, if it somehow was then that probably wouldn't be the thing Estha wanted, because that's messed up. Anyway, Merrin really feels like the problem here is all the cognitohazard stuff that Estha can't - or won't - tell her about, and she can't unilaterally decide that they're going to be fully open with each other now, and one-sided complete openness with him is...not, really, something that appeals to her right now.)
Merrin has concluded that the best thing she can do is to be okay, on her end. To be reliable and predictable and super on top of the logistics that are in her purview, and to be uncomplicated to coordinate with and handling her emotional support needs on her own rather than flailing at him across a culture gap and falling into metaphorical spike pits.
(This is maybe slightly a self-serving conclusion, because doing that is easy and comfortable for Merrin, whereas having a fully open conversation about how Laeirthe is in her head and that might imply things about what the [Outer Gods] want here does not sound easy or comfortable at all. But Merrin has poked at it and concluded that that doesn't mean it's the wrong conclusion.)