Frankly, if we needed it quick and dirty, she could be a Snake echo with just the special moves changed to have the Smash 4 assist trophy and replace Cypher with a T-copter and it would work fine, but I think if any Wars rep gets in the game, the concept would have to match their strategy roots.
Cheezey Bites
said over in the Isaac thread, the best representation would be a summoner character with a focus on stage control. Special moves all summon different units as 2D sprites, have a funds meter like Hero's MP so you can't build a bajillion units and to incentivize things other than camping.
Oh, they'd likely be the most toxic, campiest character in the cast, but you could do it in a way to promote strategy. Strategy, strategy, strategy. Send in the tanks against Sonic charging spin dash, send in the fighters or AA against Palu to shut down her air approaches, artillery against big and slow characters, ect. Force your opponent to not play their game.
Of course, these concepts could all apply to Andy and then Sami as an echo fighter would just have weaker tanks and direct fire units while having stronger infantry, so she'd be more prone to laying down lots of the weaker/cheaper units and ranged.
In the same way, I'd kind of be bummed if the only Djinn in Isaac's kit shows up in his taunt or something. It really needs to be his gimmick, in whatever form it takes. You could make him just use Psynergy and be great, but djinn would make him completely unique and represent the series best.
But for both of them, I'm just worried about them being chosen as it's been almost a decade now since their DS last gasps. Sakurai has shown that he'll pretty accurately capture the essence of any game in the fighters.