Sheila R. Lamb
Researching a Goddess
One of my favorite sources when researching for the Brigid stories was this paper by Dr. Lisa Bitel. She's a professor of religion and history at USC. Her work on connecting Brigid the Goddess and Brigid the Saint was right up my alley as I followed intuitive leaps for the story ideas.

I should note that, in the beginning, Once a Goddess, Fiery Arrow, and Church of the Oak were all one manuscript. I wasn't planning on a trilogy. I just kept writing. Once a Goddess was born out of a one chapter flashback scene in Fiery Arrow, and well, here we are.
Back to Dr. Bitel's early paper. It focuses on the work of Cogitosus, and how early hagiographers incorporated early myths in medieval saints, at a time when no women in the Church had been given sainthood.
But Brigit's hagiographers also invoked prechristian history in their allusions to the landscape. Once, heroines, warrior-women, and territorial protectresses from the myths and king-tales had wielded feminine power in a land that denied women political authority. The extraordinary females of the ancient past, relics of an already lost pagan Ireland, supplied possible models for a saint who did the same. (Bitel 2001)
It's perhaps more logical to think that the pre-Christian beliefs were incorporated later into the Christian. This seems to happen in Rome, for example, and the scheduling of holidays such as Christmas/Winter Solstice, Easter/Spring Equinox or Beltane. But Dr. Bitel poses the question: what if the opposite were true? She concludes with this:
But in fact, the hagiographers knew exactly what they were doing. They were not transforming a goddess into a saint. They were casting a saint as a goddess. They were making a case, as writers of saints' lives must do, for the superior virtus of their subject... What is more, their saint, their churches, and their political allies were competing for souls with Patrick and other male saints and stronger kingdoms. Although they lost the battle for leadership of Ireland's churches, the tactics of Brigit's hagiographers made Kildare one of the ecclesiastical centers of Ireland throughout the Middle Ages. The hagiographers also gave us the goddess Brigit. (Bitel 2001)
In this paper, the idea is that hagiographers created the goddess in order to strengthen the nun, who is now a saint. If this is so, their gamble worked.