She's the main character of the recursive fanfic "Fallout: Equestria - Project Horizons", the single largest and most popular story based on Kkat's "Fallout:Equestria". Knowledge of the latter is not necessary for understanding of the former, although basic knowledge of the "Fallout" and "MLP:FIM" series' would be beneficial.
How many can compare to one who, even when the odds are all stacked against her, could still prevail? How many are brave enough compare to one who, even though she had committed countless mistakes and done so much wrong, is willing to face up to her errors even though she may never make up for them? How many are strong enough in their convictions compare to one who, regardless of what horror, pain and evil thrown in her way and made her suffer, still strive to do good, and be good?
Blackjack - may she persevere, may she triumph, and may she one day find peace.