...Yeah no. I want this smart, wise, and kinda silly guy to be the new king.
She should really just be honest with him and say she doesn't actually like his brother. I don't think he'll disagree, and he's been pretty understanding so far. And that means he can propose to her himself and become the next king.
I get that she's separating fiction from reality, but why doesn't she pursue a different route again? She's already disinherited, and she clearly likes at least the concept of the other guys-one of whom was willing to be a commoner with her.