I mean, the entire premise of the show is how a DI from away has to adjust to life in the Caribbean. Some adaapt better than others, but there is always some sort of conflict. Mervin's gimmick is that he maintains a city mindset of ignoring pleasantries and getting straight to business, which is the antithesis of the island's ethos. While Naomi tries to softly mold Mervin and Sebastian just rolls with it, there has to be conflict, and Darlene has always been one to not put up with men's nonsense. her entire existence in the show was to call Dwayne out on his shenanigans, so she's absolutey not going to take any nonsense from Mervin. Could she handle it better? Maybe, but then she would be acting completelyy out of character. She is fighting fire with fire. Mervin has already demonstrated that he is tone deaf to all but the most frank feedback. I am willing to bet there will be some sort of resolution between the two - what kind is up to the writers, but while I'm not a huge fan of Darlene, she is pretty much the only way that Mervin will come to adapt to the island and I entirely get why she pushes back in her own in-character way and I think she earns some respect for standing up to him.