unless you filed an injured spouse allocation form https://www.irs.gov/pub/irs-pdf/f8379.pdf with your return, the IRS will seize the entire refund if it's less than the child support owed.
the ISA won't do any good unless you have your own income.
If you are filing Form 8379 by itself, it must show both spouses' social security numbers in the same order as they appeared on your income tax return. You, the "injured" spouse, must sign the form.