Britney Dunlap is the kidnapping and rape victim of pedophile Carl Dunford, abducted when she was ten and held captive for five years. She was brainwashed into having Stockholm syndrome, a sort of "sympathy" she was conditioned to respond with Dunford wanted to continue the rapes and captivity.
When Dunford told the then-teenage Dunlap he wanted another younger girl, she broke free from the oppression of Dunford's erotomania and captivity and snapped. Turning the "rejection" into facing her trauma and fighting to escape, she stabbed Dunford to death and castrated him, throwing his tarp-wrapped corpse into a river to not sit with the carnage. Not knowing where to go, she ran to a small forest shed she loved to go to as a child with her friends.
Benson and Agent Dean Porter tracked her to the shed, where she recoiled and was terrified post-trauma, afraid to go back home when she heard they came to rescue her. She was brought into interrogation, and in socially-awkward and scarred episodes, she refused to look at or talk to the two. When Benson was alone with her and offered her fast food, she started going into details, first confused about the murder and saying she "loved" Dunford, but finally breaking down facing she killed Dunford out of revenge and to prevent the trauma of other children. Benson gave her comfort as she cried from facing the truth.
Reuniting with her parents and discussing with the local DA, she was never charged and immediately arranged to receive psychological diagnostics and treatment for her trauma (SVU: "Infiltrated")