If that's Alexis, then think of it this way: Jaden's rival, the spikey, black-haired dude who went around to conquer all of the other duel schools ended up wearing the uniform, which was black. From what I remember, that episode had nothing but male duelists.
Maybe the artist decided he wanted her to wear the female version of that school's uniform. From what I can see on his pixiv page, he seems to like the guy and has drawn him in many different dueling outfits, one of which being a black and white suit ensemble like hers. He also made a mini-manga in which one scene the guy daydreams about being married to her. He make like that pairing, which is why he put her in the same uniform as his.
It at least makes better sense than picking a random outfit for her and not going with the normal schoolgirl pattern.
