It's not actually reasonable to be finding this interaction as enraging as she is, Merrin tells herself firmly. Her frustration isn't really in response to any of what Estha is saying, which is - reasonable to bring up from his own perspective, and helpful information to have on her side, and she's somewhat confused on what he even wants to get out of arguing with her, what's even the point in convincing her not to try when, if he's right, he can just let her try and fail, but it's in expectation probably going to help if he's willing to talk to her and she can get more information, so she should do the thing that achieves her goals and not tell him to please go away...
She's been awake for a pretty long time, hasn't she. Ugh, she's going to have to go back to budgeting time to sleep, now that she can't just almost entirely replace sleep with powerful healing magic. Anyway, it makes sense that she's cranky and a bit stupid, but Merrin has trained on scenarios where she had to do objectively harder things than having a conversation with someone she's mad at, while objectively more fatigued than she is right now. Stop whining and just do it.
“Oh, so trapping a soul is a thing in principle," Merrin says sunnily. "I wasn't sure. I don't have access to wizard spells right now, so unless that changes I would be trying to figure out something non-magical, which probably doesn't work at all but if it did work it would have different constraints. ...It's unclear to me why Asmodeus would prioritize tracking your soul down on another planet if he didn't think it was worth Aspexia Rugatonn's spells to get you back alive? You would think a living 6th circle cleric would be more valuable to him than one more soul out of trillions."
(Does the Share Language care to inform her what in the world a "Morrigna psychopomp" is, or a "Marut inevitable"? Are they the sort of thing that could annihilate Merrin from existence, because as long as there's still a Merrin, she's going to keep working on trying to make it so there isn't a Hell anymore in a thousand years there are all sorts of ways for Merrin to stop existing, it might even be the default outcome here, she has no idea how the ending-up-here thing worked, she doesn't know that she'll respawn on another planet again if she just dies here. But if she DOES then she will be VERY ANNOYED and then she will get back to work on her stupid enraging research project of finding Golarion and recruiting allies and solving their Hell problem.)
"...It's not a -" crux? no one-syllable word for that, "- a deciding factor, for me, whether this is actually possible. In my culture, a legendary hero," SEE KALORM SHE SAID IT WITH A STRAIGHT FACE, SO THERE, "would never just take at face value that a problem was impossible, if it was important, and this is important to me, and if I'm going to be stuck in a stupid ridiculous game played by an Outer God then I might as well stop whining about how I don't like it and try playing to win. You might've had more luck convincing your Mariona to be more ambitious if you could've given her a project she would actually want to succeed at. That being said, I do wonder if it was in the interests of your," word for 'the Governance-like organization working for Asmodeus?', "- of the church of Asmodeus, to conceal information about solutions and convince you it's a harder problem than it actually is."