She wasn't born of a virgin, that I'm aware of; and I don't know HOW it came to be that she was free from original sin. There is, however, an excellent book on the subject. Parts of it were recently made into a movie produced by Mel Gibson. The book is much better, however, and more complete.
I heartily recommend it to you! From the excellent research skills that you displayed in the Evo threads, I'm sure you would be more satisfied to research it yourself rather than take my word for it, anyway. *VBG*