Nefris is a minor NPC in the Mask of the Betrayer campaign. She is a powerful Red Wizard of Thay and headmistress of the Academy of Shapers and Binders.
Nefris is Safiya's mother. Upon reaching the Veil Theater in Mulsantir, you learn that Araman has led a coup in the Academy and killed Nefris.
Later on you learn that Nefris was a partial reincarnation of the Founder.