Goddess of Yesterday by Caroline B. Cooney tells the story of a Anaxander in ancient Greece. Taken at age six she is forced to live on an island. As time goes by the island is attacked. She pretends to be Medusa to ward off evil doers. When she is rescued by a King she decides to take on the identity of a princess and of course is treated royally - this girl is a survivor! She meets Helen of Troy and life becomes even more complicated.
You may recognize the author Caroline B. Cooney who wrote the The Face on the Milk Carton series a modern story.
If you want more tales about mythology and ancient Greece try Troy and Ithaka by Adele Geras. You may also want to read Noboby's Princess by Esther Friesner or Quiver by Stephanie Spinner you can be sure the gods and goddesses will stir things up just for their own entertainment.