How to pay employee called in during PTO leave

Q. We have a nonexempt salaried employee who normally works Monday to Friday and is paid biweekly. She took a week's vacation, which would come from her PTO (paid time off) bank. We had a customer emergency and called her into work on the Saturday of her vacation week. How should she be paid? Should she receive her PTO pay but have eight hours less of it charged against her PTO bank? Should she be paid for eight extra hours, plus her week of PTO pay? If we pay her both PTO and eight extra hours, do we have to pay her overtime? —W.M.