All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
Having children is the right of both husband and wife, and it is not permissible for one of them to prevent the other from this right without his/her permission as we clarified in Fatwa 87376.
Therefore, if your wife had used contraceptive pills without your permission then she has made a mistake, and if she did so while knowing its ruling, then she is sinful. Moreover, lying to her husband in order to prevent him from his right is another sin. So, she must repent to Allaah and seek the pardon of her husband. For more benefit about the conditions of sincere repentance, please refer to Fatwa 86527.
Based on this, she must obey her husband and not take these pills without his permission.
Allaah Knows best.