Jill is an infighter whose attribute is shock. If you're thinking of taking her lightly because she's a woman, you're in for a rough time. She's every bit as fast and strong as Bruce, however that's about as far as their similarities get.Jill's got a bit more defense and wisdom than her rival, but on the same hand a little less endurance. Her most standout weakness, however, is her complete intolerance to magic. Jill's resistance is very low, making her very susceptible to magic attacks. Unlike armor, which adds on defense, accessories simply amplify whatever your natural resistance is. This makes Jill's strategy against magic users "KO before they can attack". Since magic casters usually have low defenses, this is completely plausible.
I think it's rather ironic that those who share her attribute, Jonas and Ariane, are both magicians. It'd be difficult for Jill if they didn't get along very well.