I feel Duroa is completely justified in her anger here, she spent years trying to build up her friendship with Nocton, and for so long Nocton refused to call her by her first name and is only now acknowledging their relationship as adults. Nocton fucked up big time and his friendship with Durou is breaking it off as a result.
What was left for Durou to admit she messed up even befriending him and remembered more of the fragments of the book she once read but couldn't recall. Of how Nocton was the villain. What else is she supposed to think. Nocton's actions confuse her and only now is he putting some real effort into trying to be friends. Yeah of course she calls bull. What if it was a trick or something?
Nocton himself admitted he tried to brainwash her, of course, she's upset by that. And it feeds into her theories and what she's getting from her past memories and others. Her accusations seemed pretty valid especially the one about the brainwashing even as we the readers know the truth.
Remember Duroa doesn't know her immunity, she assumes the brainwashing just wore off and is taken measures now to prevent it from occurring again. Even Nocton thinks he still brainwashed her or something. And considering Nocton's treatment of her when she was younger, as brasher and dismissive. She doesn't know the extent of how Nocton was treated or thinking. Nocton doesn't exactly make that obvious.
Of course, she is going to stick with the OG main leads especially when they seem to respect and try to help her.
Despite our suspicions as the readers otherwise. Because we see the story as a foregone conclusion that they will end up together.
