Y'know ... I question how well Star knows Jackie tbh? The two appeared to naturally get along really well in "Just Friends", but there's a part in the book where she mentions that "she would hang out with her more if Marco wasn't so nervous around her" or something to that effect.

Essentially it boils down to out of just being courteous to Marco (because Jackie's his crush) Star refrained from getting close to Jackie up until the point the books was written (which I guess is sort of corresponded with the 3 Supercool things about Jackie list added at the end, where two of them just deal with her green hair highlight). It's likely Star's jealousy and uncomfortable-ness with the JarCo situation kept her from doing so later on.

So, yeah I do want their relationship to be explored more, but I don't know if that will be allowed to happen as long as Marco remains a barrier to that. On another related note I sort of also question how wise it was for Star to try to play matchmaker to Jackie when she apparently doesn't know her that well? I sort of wonder if that element is going to come up, especially if Marco did fail to live up to his confession to Jackie and "be the one she deserves, the one who WANTS to get to know her"?