I'm sure this will work out somehow for her but seriously, girl, he just wants you to be there for him. It's not doing anything for him if you get yourself killed besides probably just pushing him to the edge. I don't get why she doesn't see her being there as a worthwhile contribution to the king despite everything he's said to her and the things she's seen herself since she was taken in. So sure this could be helpful if she passes everything but if she were to die then it'd have the exact opposite effect she wants so it seems like the risk and rewards don't match up. Now if she was doing this because she herself wants to feel useful I'd get that sure but so far she's taking like it's really for the king when overall it just seems like a bad gamble for him considering he only gets the tacit acceptance of people he doesn't care to have approval from anyways
It's less about her wanting to feel useful but
needing to be useful.
The first chapter spells it out already: she was raised (read: probably brainwashed) to be sacrificed, to go there and die.
She doesn't have a place to return to and all the people that ever slightly cared for her are now here in the demon world.
She's pretty much comparable to a victim of a longterm abusive relationship or someone fresh out of a cult.
She needs confidence but that takes time, trust and that security. She also need to be able to have an ouce of control in the situation, some agency that let's her feel in control of the situation
Just him going "don't worry babe i'll protect you<3" while she sees all the consequences that has on the kingdom? While also caring for him as a the person he is? Somebody who cares even about the people that he only has somesort of ok relationship with?
I can see why she made the choices she did.
If anything I think the guy is somewhat at fault for being the one in "power" in this relationship and not really realising this.