Get Lucky by Katherine Center

After Sarah Harper is fired from her advertising job in New York City, she moves back home to Houston. Her older sister, Mackie, is thrilled to have her back. Mackie has been trying to have a baby with her husband, Clive, for six years. At loose ends, Sarah figures she can acts as a surrogate for them. Living with Mackie and Clive for nine months might be a little too close for comfort, though. Sarah's life is also complicated by the reappearance of Everett Thompson (the high school boyfriend she dumped but who is now gorgeous). Will Sarah be able to get her life back on track and can the sisters relationship survive Sarah's generous act?