>>112020531>she took herself out of the way so Marco could get with who he truly wantsI get that out of universe it can be put that way, but in-show it wasn't really played as, like, Jackie telling Marco to go to Star so he can be happy. It was her being unhappy with his feelings for Star and ending it before it got worse. I think that gave her more depth than either her just being happy about Marco's feelings and willing to assist in them, or acting jealous because it would've made for too easy an out (ex. she's shallow).
>She has no other discernible character traitsI'd say she does. Outgoing, part of her interactions with Marco are her wanting to help him break out of his shell. Still relates to Marco, yeah, but it's more than just existing as his girlfriend.
>no episodes with her as a protagonist or a participant in anythingI think there are plenty of characters that never really got played as protagonists, or just existed to serve their narrow roles. Not really defending that so much as saying it's natural if they're not the protagonists or central to the larger plot. As a participant in anything, some of the S1/S2 school episodes sorta did.
Even with all this, I'm not at all saying she's the best written character in the world or the show, and I'm not even a huge Jackie fan. I just think she does have a character and that her plot would go pretty differently if replaced with someone else or if they did the absolute bare minimum with her as a love interest once the relationship began (they kind of did with number of appearances, but what I mean specifically is that they could have had Marco actively break up with her, not had her even appear again in S4, or just played her as a cheater/jealous harpy to get rid of her easily). Again, not the most interesting character but I still think she has one, even if "genuinely nice person who still has her own standards" doesn't stand out much in shows where it's often expected everyone will be crazy or an asshole.