V.C. Andrews 
Celeste 

He was her mirror image. Now the mirror has cracked.Celeste and her twin brother, Noble, are as close as can beuntil a tragic accident takes Noble’s life. It’s a loss that pushes their mother, a woman obsessed with New Age superstitions, over the edge… Desperate to keep her son "alive, " Celeste’s mother forces her to cut her hair, wear boys’ clothes, and take on Noble’s identity. Celeste has virtually disappeareduntil a handsome boy moves in next door, and Celeste will risk her mother’s wrath to let herself come back to life.