You know what? I don't even blame her. It takes a certain type of person to become their own independent, self-reliant person despite being pampered and coddled their whole life.
Her family didn't prepare her at all to lead in the event of any of the men dying. They didn't train her at all in anything remotely close to combat or self-defense. She was raised to be as innocent and sheltered as possible, get married to the prince of another kingdom, have kids, and be secure in that. It was both because they cared for her, but also for political purposes.
I'm not mad that he basically told her to give up and find someone to marry. She is what they made her, and he doesn't expect her to be anything else. He also likely can't stand to send a nineteen year old sheltered princess with no skills whatsoever to kill what is supposed to be a nigh-unstoppable demon lord who just trapped him in ice after stealing his "heart", and toppling their kingdom. Honestly, if I was one of the characters in this story, I wouldn't expect anything from her either. It's obvious how this story should go as a reader, but as a character in the story I would be no different than the ministers in not believing she could do anything. I mean, she can't even lift a sword, and was pushed to tears just by being called an idiot. At nineteen years old.
So no, I don't blame her at all. I don't blame him for basically telling her to give up and find a way to survive, and to live in happiness. I DO blame her family for not preparing her to even somewhat lead a kingdom in the event of an emergency, for coddling her her whole life, and for basically enabling this event to happen in the first place by catering to her wishes no questions asked, at the expense of quite literally the entire kingdom, if not the world.