Tess is an elven cleric long thought dead by McDermott
Tess has been held prisoner by the ratmen of Calli=Pygous for decades, forced to do their bidding upon pain of death. She long ago stopped worrying about and even asked for death but her captives keep her alive just to torment her.
She sometimes complies with their demands to work magic for several reasons. First, it delays the ritual rape of her frail body but more importantly, seeing her prayers answered by her gawd (Luna) makes her feel that there is still hope and goodness in the world and that she is not wholly abandoned.