The phantom twin

"Isabel spent her life following Jane's lead. Literally--of the two conjoined twins, Jane was always the stronger one, both physically and emotionally. But when Jane dies on the operating table during a risky attempt to separate the twins, Isabel is left alone. Or is she? Soon, Jane returns, attached to Isabel from shoulder to hip just like she used to be. Except Isabel is the only person who can see Jane--a ghost, a phantom limb, a phantom twin"--Provided by publisher.