That is not, I repeat, not the implemented mechanic. The slave will always move towards the boat. She doesn't follow you. You follow her and drive her in front of you with your crop. It does rely on NPC pathing. The only thing you control with your crop is her speed. It's normally 0. When you hit her, she starts running (towards the boat!), then after a while slows down to walking and then standing still again. And then she needs another reminder with the riding crop. She will find the correct w