The character flaw in Ember's case isn't the penalty to rolls, it's how her designed build doesn't fit her personality. She is a child-like character who preaches peace & forgivness, and yet in combat turns enemies to cinders screaming "too late for apologies". She would have made more sense with a patron that grants healing or protective spells instead of hellfire rays.
What she preaches depends on your choices. You can turn her into a "And if you don't listen you burn" kind of preacher. So the potential indicated by her combat dialogue is there.
