"City of Heroes"
When a random bullet from a street fight results in the death of her son, Frankie Kemp decides to become a "hero". She dons a costume and takes her fight to the streets, doing things the police can't do to apprehend thugs and criminals. She is dubbed "Chance" by the tabloids, "She likes to take a chance."
Then the North Koreans unleash a virus that has no affect on some people, kills others, or genetically enhances some. The virus had no affect on her, so now she faces superpowered villains using only her wits, skills and experience.
Contemplating hanging up her costume and cape, she gets the news that the convicted killer of her son has acquired powers and escaped from prison. So the costume comes back on and she goes in search of Eric Black, now calling himself Shadowslide...