Has she been diagnosed as sociopathic? The problems with emotion could be a lot of things, such as Asperger's or a nonverbal learning disorder. People who have this have a lot of trouble interpreting emotions, which would explain her apparent lack of emotion or her labored smile. The charisma you describe could just be her coping mechanism to make up for the fact that she really doesn't understand how social interaction works.Don't let your friend stay with you. Unfortunately, she will need to seek help herself or else be committed again.