Unfortunately, her salary is irrelevant to child support, and it cannot be attached. You may have the right to increase child support, but it doesn't sound likely because he isn't working. Most likely, your support would be reduced. His acting as a homemaker is a legitimate status unless you can prove that he quit work to avoid paying child support.
Your ex-husband is required to assist with child support his child. He is not able to become a "house husband" if he has current responsibilities he needs to meet. I would file a Motion for Contempt on the issue of child support, if he is not paying the amount he owes and making payments on the arrears. You will not be able to attach her salary, but the court may order him to go back to work to pay his support obligations.