Dreamsnake by Vonda McIntyre...
They called the healer Snake and she bore the name proudly, for the medicine she distilled from the venom of the viper she carried with her was a portent cure and a soothing power to her other companion, the alien dream snake, banished fear. But the primitive ignorance of those she served killed her dream snake and wrecked her career - for dream snakes were rare and Center would not grant her another. Snake's only hope was to find another - and on her quest she was pursued by two followers, one driven by love and the other by fear and need.
