My thought is that when they are controlled, they can't hear or see anything the person controlling them doesn't want them to see. Like they are disconnected from their senses.
She might not have a great plan, maybe it's just the best bad plan. Also, any plan with Arim can't be directly offensive. If she won't attack, she can't sneak attack.
Holiday theme change,
Anyways, I wonder what their plan is going to be? Why alert everyone with that whistle?