After watching the final episode it all makes sense now why Joo Ran took that step for Ep7 ending....When she asked sang eun in ep7 if she feels better after killing her husband sang eun replied with her life has not improved in any way thats what made Joo Ran to make sang eun's life better and the only way to do that was insurance money .... She made sure at Ep7 ending Sang Eun gets to be a victim then only the police will get that Sang Eun's husband got killed by Joo Ran husband ....She just choose to protect that one Woman and it was Sang Eun but in her own way