I posted this elsewhere, but the character Shae may have been inspired by one of France's most infamous poisoners, Catherine Deshayes:
http://murderpedia.org/female.D/d/deshayes-catherine.htm
Catherine Deshayes, sometimes known as Catherine Monvoisin, or simply La Voisin was a French serial killer. She was born around 1640, and executed as a witch on 16 February 1680, in Paris; together with several others. She played an important role in the so-called Affair of the Poisons. She lived from charging high fees to make horosocopes. She celebrated black masses, practiced abortions, sold love potions and poisons. She is said to have sacrificed infants.
Pronouned with the silent 'S' in French, so clear similarity there. It's also been speculated that Shae may have had a hand in one or two of the poison plots going on in Storm of Swords. There's admittedly a lot of Melisandre in her as well, though.
I really love the idea that GRRM has been seeking inspiration from women in history who were instigators and masters of their own fate - even if Deshayes was on the shadier end of the scale. It makes the books that much more grounded in reality.
