I think both of them are wrong. The priest is kinda right for saying how jeweled eye ppl will be very useful. However, no child should ever go to war at such a age..
The dad is being too protective. He's doing right as a father, but he should know he can't protect her forever. He has to slowly let her learn.. But given how she's very cautious right now. I guess it's understandable?
I think both are right. The father wants to protect the found daughter who has already suffered much, and would suffer even more helping people, because they would know she have jewel like eyes and she would be persecuted by people who are greedy for her powers. And the priest wants to save many people with her powers, with the ideia of "sacrifice one pure soul to the good of many others", the famous mártir.
Is he actually a bad guy or something? Because I mean he does have a point they do need her and her eyes to be able to stop the demon I get that she is just a child and I know that all jeweled eye users have sad deaths but still it's not like it is just some small matter? The demon is already inside the castle and I'm sure people will start to become infected if something is not done for example one of her siblings? Or her father? I mean anything could go completely wrong if she goes but it's going to be a hell of a lot worse if she doesn't go