Not a plot hole. They all knew this would be the case, but the King felt that it was a necessary sacrifice in order to keep the army from being raised.
And FURTHERMORE, this is my signature! SERIOUSLY! Did you think I was still talking about my point?

Because she had to see the crown piece safe first.
It's not nihilism if there's a question mark at the end.

But if she was so at piece with dying. Why did she not kill herself earlier, in order to stop him
"It's a big rock. I can't wait to tell my friends. They don't have a rock this big."

When the sentence is first given he asks her if she is at peace with the decision and she said she is. It was all about the wording, being at peace with a death sentence not just agreeing with their father. The king and daughter probably had a long talk and especially since she is all about peace, considered it to be for the greater good.