The Other Twin — Katherine Stone

Thirty-one years ago, after an accident on a California highway, a woman goes into early labor. Her baby survives. But her husband dies.

Today Paige Forrester is a doctor, like the father she never knew. But Paige herself has medical problems, which she's been keeping a secret. Her life becomes even more complicated when she meets Gwen St. James, a woman with secrets of her own.
Gwen is an accomplished makeup artist, a vocation she chose because of the birthmark that disfigures her own face. Gwen, whose past is filled with questions, has never learned the identity of her parents. She's completely alone, a woman hiding behind a skillfully applied mask.

Paige and Gwen become friends, confide in each other, grow close. As close as sisters...