Originally, Satan Girl was an evil duplicate of Kara Zor-El created by red kryptonite in Adventure Comics #313. She attempted to kill Supergirl's fellow female Legionnaires so she could sustain her independent existence. Satan Girl reappears in Legionnaires #17, as one of the time anomalies created by the events of Zero Hour. The storyline in Supergirl vol. 5, #3–6 is inspired by the original Satan Girl story, with black kryptonite producing a duplicate "Dark Supergirl".
Delores Pratchet
Dolores Pratchet was the post-Crisis on Infinite Earths Satan Girl, appearing in Supergirl vol. 4, #40–41. 200 years ago in colonial America, Dolores Pratchet, a practitioner of Satanic rituals lost her daughter Rachel when the young girl tried to save her friend, a slave named Ember, from being burned at the stake for witchcraft. The two girls fused into one and became an Earth-Born Angel of Fire. However Ember began to fall from grace, dooming both her soul and Rachel's. Dolores made a deal with the demonic Carnivore and agreed to become his servant to save her daughter. He gave her magical powers and dubbed her Satan Girl. Satan Girl's magic was able to bridge time and pull the current Angel of Fire, Supergirl, from the present and switch her bodies with Ember, so that Supergirl would die on the stake, and Ember would exist in the future. This disturbance of the timeline allowed Satan Girl to appear in the present with Ember. However Supergirl was able to escape her death with the aid of Ember, who returned to her own time to live out her fate, and a sorceress known as Tammy Neil. By setting the timeline right, Satan Girl crumbled to dust as she was not alive in the correct timeline.
S'tanicule Gyrstress
This Satan Girl is from another dimension and is referred to as the Brocian goddess of love and death. Brainiac 5 blasts an old Brocian statue dedicated to her with chronon energy, ripping space and time and allowing her to free herself. She unleashes a crimson plague that makes the world love her as she primes the world for her people to take over. Supergirl and Brainiac 5 channel the time energy that freed her to send her back and trap her. She appeared in Supergirl vol. 5, Annual #2. Her appearance is similar to Dolores Pratchet.
The first Satan girl had all of Supergirl's powers; see Powers and abilities of Superman. The second Satan Girl had various magical abilities, such as the power to cast spells and switch souls. Her trident fires blue flames that can burn through almost any substance, and is strong enough to pierce invulnerable skin, such as Supergirl's.