The female lead in 'The Nightmare Before Christmas' is Sally, and she's way more than just a love interest. She's the emotional anchor in a world that's basically built on chaos and scare tactics. While Jack's off having his mid-unlife crisis trying to kidnap Santa, Sally's the one showing actual concern for the consequences. She's quietly rebellious, making her own path by literally sewing herself together and escaping her creator, Dr. Finkelstein, over and over.
Her role is the voice of intuitive wisdom. Everyone in Halloween Town is blindly following Jack's dangerous new passion, but Sally sees the disaster coming. She tries to warn him, tries to fix things, and when it all falls apart, she's the one who actively saves him. She isn't waiting around to be rescued; she's doing the rescuing. The story needed that grounded, caring presence to contrast with Jack's manic ambition, otherwise it'd just be a tale about a guy who ruins Christmas and gets away with it. Sally provides the heart, and the moral compass, that the film would feel hollow without.
Honestly, a lot of early animated female characters just existed to be pretty or get saved, but Sally had agency. She made choices, took risks, and her love felt earned because she challenged Jack, not just adored him. The story wouldn't have the same emotional weight if she wasn't there to literally pick up the pieces.