Divine by Mistake - P. C. Cast - Bog

Surrounded by old folks and even older artifacts at an estate auction, Shannon finds an ancient vase, complete with a beautiful painting of a goddess that looks just like her. And just as she's stealing away with her purchase, she's magically thrown into the world of Partholon, where not only has she taken the place of Rhiannon, Goddess Incarnate and Epona's Chosen, but she's due to be married to a surly High Shaman centaur, ClanFintan.