"They do this by arranging for Tan to "kill" Lessie, then spiking Lessie with the Autonomy spike(s) to drive her mad. In her Autonomy-driven madness, she is set up for a collision course with Wax, being careful not to reveal her nature until the end. Then, when Wax realizes what he has done, Odium comes in and sucker-punches him in the same way he did Kaladin and Szeth."
Harmony arranged for Lessie to be killed. So Wax would go back to the city. The book mentions that Bleeder has commented on Harmony forcing her to do something in the past, I do not remember the exact wording. I am pretty sure this was when she "died" Bloody Tan was controlled by Harmony to do so because she fell in love and would not allow him to return to the city. She stated that she could never take him from the Roughs because he loved it there. This is why Harmony "controlled" her. He didn't do it directly, but he still controlled her just the same by controlling the events around her.