Dreamsnake, by Vonda McIntyre. This won both Hugo & Nebula Awards for best novel. A fix-up incorporating "Of Mist, and Grass, and Sand" (a Nebula-winner), "The Serpent's Death," and "The Broken Dome" (all from Analog) - with half the book original.

The healer, Snake comes to Arevin's clan to help a dying child. In her world, healers use the twinned snakes as more than a symbol of their profession. The cobra and the rattler are essential to their work, as is an offworld creature, delicate and hard to breed - the dreamsnake. When Snake's is killed, she feels crippled; she believes she has failed as a healer. But she is offered a chance to obtain another dreamsnake, and though it means a long and dangerous journey, she eagerly accepts. In her quest she encounters the gentle desert folk; the inhabitants of Mountainside; and the families of Center, who no longer care what happens in the world outside their city's gates...