Emily Hanlon
Circle Home
1981
from the dustjacket:

Mai is thirteen, and alive in the body of Isabelle Lessing. Everyone — Isabelle's loving parents, her brother, Paul, her classmates and her friend Mr. Krigorian at the pet store thinks Mai is Isabelle, who fell from a second-story window four years before and was pronounced dead at the scene of the accident. But "Isabelle" revived.

Even though all her memories before the fall are of another time, another place, Mai has come to believe what everyone believes — that she has always been Isabelle Lessing of White River, NY. She gives up her dream of an earlier world. No one around her knows anything of a girl called Mai.

Only Ogon, a snake, seems to know. Once they meet, Mai senses with joy that Ogon has come to fetch her "home" to the world of her memory, where peace is a way of life and fighting among people is unknown. Does such a world exist? Is it possible to leap into the Stone Age from the confinement of a present-day shopping mall? Mai, with Paul, unearths the unearthly answers. Then the girl called Isabelle must choose...