her Defense is 500 so let's say she can mitigate 500 damage. her HP is 700, so a fire lance (1200 base damage) from the MC at level 1 still can kill a level 65 tank. Imagine a game where a level 1 can oneshot a level 65.
@ziel depends how defense works in this world. If it's like other games it's a stat used to derive a percentage of mitigation. Also her personal defense is 500, I'm guessing it doesn't include the shield.