can my ex reinstate my child support payments after she waived them

If there was a child support order through the Texas Attorney General because the children were on any type of public assistance, she could not have waived the money owed to the state. She could certainly waive child support owed to her. If she did not pursue child support and there was no order, she cannot go back to try to collect it. But you have to know whether the children were on any state aid and whether the state has been trying to collect support from you.