I mean... You usually figure out what someone thinks of you by 1) what they say to you, 2) how they treat you, & 3) what others suggest.
Based on their history, Duroa’s distrust & suspicion for Nocton are completely reasonable reactions. Not that his actions would be excused or erased by knowing his motivations, but she doesn’t even know the why. All she knows is how poorly he’s treated her in the past, & how callously he treats others.
It’s frustrating, but her defensiveness is warranted. 😥