My husband pays his ex child support, support owed, child will turn 18, then what happens?

Q) My husband pays his ex child support. She has been ordered to pay (by magistrate) uninsured medical expenses – they are reducing her child support that she received by 20%. However, the child will turn 18/graduate this June (in four months) and the reduction in child support will not even come close to covering what is owed. Then what happens? What options do we have for collecting.

A) Once a child is considered a legal adult, the non-custodial parent is no longer required to pay child support payments. However, should there be back child support payments that remain unpaid, the custodial parent still generally has the right to collect on these back payments, even after the child has been emancipated. Source: http://www.crckids.org/child-support/eligibility/collecting-back-child-support-payments/