Mairead Philpott has said she was stunned when Lisa Willis left Mick Philpott and the family home with her five children.
Asked at Nottingham Crown Court: "On a scale of 1-10 how surprised were you that Lisa left?" Mairead replied: "10".
Mairead Philpott said she and her own six children were left distraught and "heartbroken" by the group's departure in February 2012.
She told the jury her children often went to bed crying, had nightmares, and some even wet their beds after they left.