Illithia's mother was an elven prostitute, barely surviving in Westcrown. One of her clients was a man of some reknown - a noted actor and a popular figure among the common folk. When Illithia's mother discovered she was pregnant, she duped a Cleric of Shelyn into casting a divination to discover the father.
Armed with knowledge - and the threat of a bastard child - Illithia's mother confronted the father, demanding marriage. Instead the man paid her off for her silence.
Sadly, Illithia's mother died in childbirth, leaving behind the gold and naught else. The Cleric of Shelyn who was duped took pity on the infant and adopted it, raising it in the temple. She used a little of the money to help raise the child, but saved a good deal to grant as a gift upon reaching adulthood.
As Illithia grew, she began to realize that hers was not a normal life, but rather a blessed one. By all rights, she should have died the night she was born, freezing to death in the streets. She had so many oppurtunities for beauty as she grew, and she saw that others in Westcrown did not share all her blessings. So she asked Shelyn to guide her to a way to help the people. To bring beauty to the world. Shelyn's answer came in the form of her skill with the glaive, and the beauty of her voice. Illithia knew that the day would come when she would fight the evils that preyed on folk. Until that day, she would sing to raise their spirits.