Making her kill Chompoo didn't make sense to me. That's the only thing that bothers me. Chompoo even said that she didn't keep quiet about the abduction. Sure she forgot that part of her memories but she did run after Rin. (It was too late, but she tried)
Also, Rin was the one who betrayed Chompoo's trust ultimately. I know that doesn't compare to Rin's death, but I think they were both in the wrong for different situations. If they had talked to one another, maybe Rin wouldn't have died. If Rin had allowed Techin to tell Chompoo from the beginning, maybe Chompoo wouldn't have been so hurt she sought payback. Chompoo's death was unnecessary. But I guess they wanted Rin to exist alone to repent her sins for eternity. Therefore, they needed a lead to kill Techin off.