Translator probably misunderstood. Jinhwa's mother is her biological parent, and Jinhwa called her "stepmother" in a sarcastic way to compare her with cruel stepmothers from fairy tales, who force their daughters to work(get up and go to school in her case). So, if no weird plot twists occur, Jinhwa is not adopted and has no stepmother.
Translator probably misunderstood. Jinhwa's mother is her biological parent, and Jinhwa called her "stepmother" in a sarcastic way to compare her with cruel stepmothers from fairy tales, who force their daughters to work(get up and go to school in her case). So, if no weird plot twists occur, Jinhwa is not adopted and has no stepmother.