I have to wonder what the author's intentions are in making Doronea appear so foolish. It has to be intentional, otherwise...
On a side note, it's a good representation of a certain side of the political spectrum.
It is hyperreality, so to speak.
The "explanation" is that even if Doronea is well educated, intelligent, and capable... she is inexperienced in the ways of the world, and because she is a girl in love she was tunnel visioning her priorities.
Dumb, I don't argue with that, but the writing style of this author does make use of this hyperreality, where certain traits are dialed to 11 at certain moments to justify certain actions.
Personally, it doesn't bother me too much... in this series, Hiroyuki-sensei is a good script writer, not perfect, but he knows what he is doing and what he wants to convey, and even with all the very well done worldbuilding... we all know what is his priority with the girls.
And truth be told, even in real life people practically stupidify themselves when they aren't looking at all the facts and let emotions run too high.