Maybe she's thick or has mental health issues.On the question of the confession, I would be surprised if she were guilty and confessed. If you have what it takes to plan and execute a murder and recover yourself so much afterwards as to be happy about it, I can't see what a few hours in police custody could do to penetrate the defences. She isnt young and vulnerable, nor is she in an overly alien environment. I want to see the terms and circumstances in which she supposedly confessed and the text itself of course.
Incidentally, how do you know she isn't vulnerable?