She's Sort Of (Okay, Really) Aggressive
Bear with us here, but one of the things we like most about Jessica is actually the fact that there are distinct moments in which she's not likable. Her storyline does not involve her trying to make friends. In fact, she often actively pushes people away as a defense mechanism.

After all, her parents died when she was young, and she blamed herself for their deaths. We don't blame her for having abandonment issues. Even as we can understand where she's coming from, due to a seriously damaged psyche, we still find ourselves getting a little irked by her own aggressiveness, while at the same time pulled in by it.

We can understand her interpersonal relationships, like with Trisha and Malcolm, through this framework, and it makes her all the more fascinating.