But Arya didn't refuse.
Since Aries proposed to bring her back in her car, then she would not be polite and take upon the other party's offer.
"Does the organization let us be a test subject just like that?" Arya asked as she entered the car. She felt that the organization's treatment was really cold. Then again, the human rights have been revised over and over after that International War but this kind of thing should still require permission.
"Don't worry, your status is different from Marco. He has been undergoing this experiment for a while and the result is quite good. But since you're a child and different from him, there'll be an adjustment needed," Aries replied.
Besides, what he meant was not to turn Arya into a stupid fool who only knew how to follow order. But to let her be more loyal to the organization. Her playful nature made it both difficult and easy for others to trust her.