Who is Thea is the novel, False Dawn?

Thea, a young woman born in 1986, is now about twenty-six years old. She was made a mutant by someone, possibly a consenting parent, in an attempt to create various types of mutants ("mutes" in the novel) who might survive more successfully than ordinary human beings in the postholocaust world. Thea has a nictitating membrane in her eye (vestigial in most people) which is of dubious value.