Yes, valid will controls the disposition of the estate. Excluded heirs may challenge the will under certain circumstances. If the estate is significant, you may wish to consult with an attorney to discuss the particulars of your matter and for specific legal advice.
The additional information you provided does not change the initial answer. Your mother could have sought relief during your father's lifetime for money owed to her under the court order. If she is still living, your mother may make a claim against the estate for unpaid child support.