I admit it's a combination of the accent and the way she expresses herself. Don't get me wrong though. IRL, I don't "hate" on folks like her, folks with a particular accent or way of talking. However, as she's a companion in a video game, it's a rather different story. I felt that "obligation" to interact with and involve her in my playthrough. I rushed past her dialogs, quests, and ignored her when I could, to spare myself the irritation, but then I'd feel like I was forced to miss out on parts of the game. So yeah, all these factors made me dislike Sera as a companion in a CRPG.

"We make our choices and take what comes and the rest is void."