What do you think of this story idea is it original should i stop?

A girl named Jessica was born very close to date with her cousin they were almost impossible to tell apart she had the same eye color as her, hair, and they seemed not to have any significant birthmarks. Jessica's mother ( Sophia ) was a drug addict who was left by herself shortly after Jessica was born, Sophia didn’t honestly want Jessica because she just had the baby so that her boyfriend would stay with her Sophia felt bad about putting Jessica in a orphanage since she grew up in one and understood how much pain Jessica would be in not knowing who her family was Jessica was born close to when her cousin was born almost to the day. Sophia decided to switch her cousins baby with hers and put her cousins baby (Marina) in the orphanage instead. Jessica grew up living like a normal teenager now 16 she was visited by Marina who was told by Sophia (when she was in the orphanage Sophia visited her and explained to her what had happened because Sophia felt bad about what she had done) Marina was about to tell Jessica's parents (really her parents) what have happened. When Jessica killed Marina she wasn’t going to let Marina ruin what Jessica thought was a perfect life.