Satan had influence over Eve before she ever ate from the tree ,deceiving her through the serpent. Putting the thought in her mind to eat the fruit without consequences. The plan was to separate them from God so that he could have influence over them. She had to believe that God was lying about the tree in order to make the decision to eat from it. Therefore willfully going against what God had commanded. She chose to believe the serpent. She made her choice, because of the idea that was put in her head by the serpent. Free-will, self-will, human-will. and not God's will.