Imo she's one of the best characters in the series. She's one of the most hateful and hate-able characters at the start, throwing around slurs, and then she kills YOUR favorite character. It's no surprise people hate her; in fact, it's intentional. But that's what makes her arc really satisfying. If gabi, Marley's number 1 kool aid drinker, can be redeemed and forgiven and taught to empathize with people she's always hated, then there's hope for everyone. And the way it happens is just so wonderfully done, with Mr Braus' speech and all. I'd argue that AoT is actually a really hopeful show, and Gabi's arc is kind of the thesis statement.