At a basic level I want to see her and the other prominent secondary characters get a bit of episode time without being the main focus of the episode. Primarily I want them to be interesting in their own right while adding to the major focus of the episode, the main characters in particular.
For Jackie I'd mainly want to see a bit more about her, outside of just how chilled out she seems to be. For example, her interest in history could make for a cute minor scene with Marco, given he's a rather focused student. I also liked how she performs a similar role with Marco that Star does, in terms of getting him to come out of his shell, but doing so in a decidedly different manner. Instead of just throwing him into a scenario and forcing him to adapt she calms him down and encourages him, it was really sweet seeing it happen in Bon Bon.
Effectively I want to learn more about her as an individual through what she can provide for the main characters.
But the rather early game-changing reveal of Stars feelings sort of put a wrench in all this, I assumed they'd wait until season 3, halfway in before they really developed that subplot. As a result it's sort of hard developing Marco and Jackie's relationship as it presents a big dividing force between the two main characters. Fuck knows what they're going to do.