The Challenger - S1.E360

A man is accused of setting fire to a cottage with his wife and kid inside. A woman walks into KD’s office claiming that he is innocent. When KD questions her further, she admits that she has committed the crime and challenges KD to prove her guilty in court. KD takes up the case, but there are clear evidences that the husband is the one to blame. Who is this girl challenging him? Did she really commit the crime, and if so, why does she come and confess on her own ?