The daughter is currently in the custody of the Pakistani government, which, as the events of the past few days have shown, is either extremely corrupt or extremely incompetent. Either way, if al-Qaeda is able to obtain the daughter, she could very well be used as a rallying point, if not trained to perpetrate attacks herself.
Fun fact: Osama bin Laden was the 17th child, out of 52, by his father and his father's tenth wife.