Will the IRS intercept my tax refund if I claim my adult student child as a dependent if she is in arrears on her federal student loan?

It depends ; the IRS can not have your refund taken to satisfy a debt you are not legally liable for;HOWEVER, if the student loan in question is a PLUS loan where you borrow money to use for the dependent's edu expenses, and you are in default of that loan, then you are legally liable for the loan and the refund could be seized.