Not much is known about Inertia's past. It was however that when the Squadron Supreme launched their Utopian program in Earth-712, Inertia became one of the members of Nighthawk's Redeemers who sought to stop the Squadron Supreme and their plan of world-domination.
Inertia (Earth 712) was created by Mark Gruenwald and Paul Ryan and first appeared in Squadron Supreme issue 10 (1986). Another, perhaps more well known, version of Inertia from Earth 31916 (Supreme Power) first appeared in the pages of Supreme Power issue 18 (2005).
Major Story Arcs
Joining the Squadron
Inertia had joined Nighthawk's Redeemers, but soon joined the Squadron Supreme as a double agent, and also started a relationship with Haywire. During the final battle with the Squadron Supreme, Inertia battled Power Princess, but was defeated by Doctor Spectrum. After the battle, Inertia and Haywire were some of the members of Nighthawk's Redeemers who joined the Squadron Supreme.
When the Nth Man threatened to destroy the universe, the Squadron Supreme went into space to try and stop him. When it looked as if the heroes wouldn't have enough time to stop him, Inertia tried to use her powers to reverse his growth. Her body could not stand the strain of the effort. Her powers backfired on her and she dissolved into a pink haze.
Earth-31916 (Supreme Power)
Inertia on Earth 31916 is a member of the US Army and a lesbian. Her very first appearance showed her destroying a bar and physically attacking several men before she was introduced to the public as part of the Squadron Supreme.
Edith's father was the head of an ultra-conservative church and a highly prejudiced and abusive man. Her powers manifested at a young age when a nurse trying to give her a vaccination could not get the needle through her skin. Her father believed this was sign of demonic power and, unable to hurt 'Eddy', would beat her mother for any of Edith's perceived transgressions.
In high school, she was attacked and raped by three boys (her classmates). While she could easily have defended herself, Edith was aware that this would only result in her mother receiving a beating and so did not attempt to defend herself. The stress of this event and her inability to use her powers when she most needed to left her in a catatonic state for sometime. Despite this, her father refused to believe she had been raped (citing the lack of injury), instead accusing her of being promiscuous.
Edith's mother soon discovered that her husband was having an affair and confronted him. Edith's father accidentally caused a car accident that killed Edith's mother and attempted to cover up the event to save his reputation. Edith recovered after hearing the news, finding and killing her father - then killing the boys who had raped her.
During 'Operation Long Walk' (the Squadron's mission in the Middle East), Edith finds a young girl whose mother and older sister were raped and then stoned to death by four male relatives on the pretext of erasing the shame of the rape ("Honor killing"). The girl had apparently been hiding to avoid a similar fate. Using Emil Burbank as a translator, Edith finds the relatives and buries them up to their necks. She then tears a steel bar off a nearby railing with her bare hands, gives it to the girl, and walks away. The girl apparently kills them.
So far, her behavior has been shown to be erratic and possibly psychotic. Stanley Stewart (The Blur) has attempted to reach out to her, and Edith has thanked him for his concern, but she still refuses his offer of friendship.