The House of Gaian by Anne Bishop

"It began as a witch hunt. But the Master Inquisitor’s plans to eliminate all traces of female power in the world have expanded to crushing the Sylvalan Barons who oppose him—and to destroying the wellspring of magic in the Mother’s Hills.

Faced with this evil, humans, witches, and the Fae become uneasy allies. But even together, they aren’t strong enough to stand against the armies the Inquisitors are gathering. So they look for help from their last possible ally. The House of Gaian. The reclusive witches who rule the Mother’s Hills. The witches powerful enough to create a world—or destroy one...

Their long-held creed of “do no harm” is about to give way to more important one: Survive."

Mass market, a nice copy!