No. Just the power of serial killing and never getting caught.(look, I know she only kills bad men, but she does it like Rorschach times a thousand, when they're helpless or unconscious, and laughing as she does)
And Miller threw the Irish thing in there because...shit, I really have no idea. Probably because he has no other way of making one woman's internal speech patterns distinguishable from another. And maybe Scarlett Johanson learned something new from her vocal coach and he's hoping to direct a movie of this.