The Margarets: Sheri S. Tepper

The only human child living in a work colony on the Martian satellite Phobos, little Margaret Bain has invented six imaginary companions to keep boredom and loneliness at bay. Each an extension of her personality, they are lost to her when she is forced to return to Earth. But they are not gone. The time will come when Margaret, fully grown and wed, must leave this dying world as well—this Earth so denuded by thoughtlessness and chemistry that its only viable export is slaves. For now Margarets are scattered throughout the galaxy. And their creator must bring her selves home . . . or watch the human race perish.