Cheryl is John Constantine's older sister, and, when John was younger, John lived with her for a little while. She had one daughter, Gemma Masters.
Cheryl is killed by her husband, Tony Masters, by wrapping an old pair of tights around her neck and chocking her to death, because he was very religious and thought she was a witch. Nergal repaired her body, but could not bring her back to life because her soul was in hell. She was a pure soul, but she sacrificed to live in hell, so that her husband wouldn't have a double punishment.
When Epiphany Greaves is back in 1979 she sees Cheryl come to John, asking if she can stay at his place with one-year-old Gemma, because Tony was being "weird". John refuses to let her stay, but offers her money to rent a hotel with. She throws the money back at him. Epiphany tries to step in and persuade John to let Cheryl stay, but he won't be persuaded. Cheryl tells Epiphany to watch out because one day Epiphany will ask John for his help, and he won't give it.