Mayu was not to sure of the plan herself but then she was not particularly capable of fighting the plant monster if it did wake and it was best to follow the orders of her sensei. Keeping Momo by her side she waits at the entrance to the cave as the others go in to gather up the plant that was needed for the cure. If nothing else she figures that if trouble really did start then she could send Momo in as a last resort to buy them time to escape.