Bella Moore is the daughter of Gillian Moore, with whom Bella was held captive by Soren and Elias Olsen. Bella was conceived from Soren raping Gillian, and they were locked in the basement of his cabin for years with other women and girls.
When Soren was found shot, Bella was revealed to have shot him to protect herself and Gillian. The police refused to press charges, and she was released. (SVU: "The Steps We Cannot Take")