Showing Sorceress of Faith by Robin D. Owens

With the world of Lladrana threatened by encroaching evil, the Sorcerers must do the unthinkable--Summon an outsider to stop the insidious Darkness slowly taking control of their land, and poisoning the Sorcerers themselves.

Yet instead of a powerful warrior, grad student Marian Harasta arrives through the portal, finding herself in the center of a struggle between Sorcerers who want to use her incredible, untapped Powers to augment their own. As she fights to maintain her independence--including facing her first magical duel--she must decide whom to trust....

Still, the Darkness will not be ignored, and a desperate Marian must offer the Sorcerers aid in order to keep alive the chance to return home. Because divided all will surely fall....