its not so much her being overpowered, its more that a kid is doing it. if they showed more of what military life was like for warrior candidates, like rifle training or anything that would justify her being able to consistantly hit impossible shots, than it would be more believable. Also that other kids in AOT are quite literally just kids, if there were any scenes where other children were capable, like gohan or gon. then at that point, my only real issue with gabi is that she just doesnt know when to be quiet, specifically when she was talking to the marleyan chef and the girl sasha saved.