C.E.) She was the one who first set forth the doctrine of mystical love
and who is widely considered to be the most important of the early Sufi
She was born between 95 and 99 Hijri in Basra, Iraq. Much of her early life is narrated by Khawaja Fareeduddin Attar. She is reported to be born free in a poor but respected family. She was the fourth daughter of his family and therefore named Rabia (Arabic=Fourth). When famine struck, she was kidnapped and sold as slave. However when she grew up, her master discovered her piousness and freed her out of his fear for God.
Philosophy: She was the one who first set forth the doctrine of mystical love and who is widely considered to be the most important of the early Sufi poets. The defining work on her life and writing was written over 50 years ago by Margaret Smith, a small treatise written as a Master's Thesis.
Much of the poetry that is attributed to her is of unknown origin. After a life of hardship she became spontaneously realized. When asked by Sheikh Hasan al-Basri how she discovered the secret, she responded by stating:
You know of the how, but I know of the how-less. 
One of the many myths that swirl around her life, is that she was freed from slavery because her master saw her praying while surrounded by light, realized that she was a saint and feared for his life if he continued to keep her as a slave.
While she apparently received many marriage offers (including a proposal from Hasan al-Basri himself), she remained celibate and died of old age, an ascetic, her only care from the disciples who followed her. She was the first in a long line of female Sufi mystics.
The Tale of Torch and Water
One day, she was seen running through the streets of Basra carrying a torch in one hand and a bucket of water in the other. When asked what she was doing, she said:
I want to put out the fires of Hell, and burn down the rewards of Paradise. They block the way to God. I do not want to worship from fear of punishment or for the promise of reward, but simply for the love of God.