Did you guys noticed the blue envelope?

I'm not really on the nurse/mother train yet but Ok Ran being instructed  to torment the husband and then torment the daughter is far more interesting/creepy than a fan gone delusional... and it would answer how she knows so many things. 

But if the mother is truly alive, and it seems she is, my question is why appear now, after all these years? For the sake of the drama? Unless her intention was never to approach her daughter and just torture her husband, but she was so obsessed and controlling with her daughter... why disappear at all?  Just because she wanted to make the husband go mad thinking he had killed her?

 Leonjhart:

I'm not really on the nurse/mother train yet but Ok Ran being instructed  to torment the husband and then torment the daughter is far more interesting/creepy than a fan gone delusional... and it would answer how she knows so many things. 

But if the mother is truly alive, and it seems she is, my question is why appear now, after all these years? For the sake of the drama? Unless her intention was never to approach her daughter and just torture her husband, but she was so obsessed and controlling with her daughter... why disappear at all?  Just because she wanted to make the husband go mad thinking he had killed her?

Initially, Only the husband was at Seongjin city so I think the first plan was to torture the husband but then the moon brothers chose to go back to their roots and then the daughter (KMY) appeared suddenly. The mother probably thought  why not kill all these birds with the same stone. Maybe she thought it would be fun to torture all of them since they are all there anyway.