She's not sure how to dress, or talk, or act around humans- and what's more, she isn't sure that she'd like to seduce and kill one. Which could prove a difficulty for her, as that is exactly the reason that she's being sent to mingle with humans in the first place. And when she ends up falling in love with the same mortal that she's placed her Mark on, sentencing him to die, only trouble can result from such a blatant breaking of demon law.