In her new memoir, ‘Ghost Girl: Surviving the Black Swan Murder,’ Eva Benefield recounts coming of age, watching her father’s relationship unravel, and pursuing justiceEva BenefieldCredit: Gallery Books/Simon & Schuster; Eva Benefield/InstagramNEED TO KNOWEva Benefield’s mother, Renee Benefield, died suddenly when Eva was just 14Nine months later, her father, Doug Benefield, married Ashley Byers, a former ballerina and swimsuit model 30 years hi…