Histrionic personality disorder (HPD)
Melisandre, aside from being the actual worst, is probably suffering from Histrionic Personality Disorder.
Affecting four times as many women as men HPD is characterised by excessive attention seeking behaviour through the use of high drama and extravagant displays of sexuality. They crave stimulation, attention and admiration and will use persistently manipulative means (such as reassuring an insecure man that he is the true king) to achieve their own needs.
Histrionic people will be overly emotional, theatrical, prone to rash decision making and likely to blame personal failures or disappointments on others.
They also have a tendency to birth spooky shadow babies. Seriously, it's in the textbooks.