When Stella was 6, she was taken from her parents by Dreykov and taken to the red room where she was trained as a black widow alongside Yelena Belova. When Stella was 24 Yelena escaped when Natasha came looking for her, but she was left behind. Not only was she trained to be the world's most dangerous assassin, but she also has powers. She got her powers from the Power Stone when Dreykov decided to experiment on her and a few other girls, but you were the only one to survive.