Hi Its common to have weakness, dizziness etc after recovery from a severe viral illness such as Flu. Its better that she rests at home for a couple of days than to strain herself. Give her plenty of fluids- water, fresh fruit juices, vegetable soups, porridge etc. Strict bed rest along with Oral Acetaminophen in right dosage thrice a day- will help her. How ever if head ache is severe, associated with vomiting, drowsiness etc or she refuses to eat/ drink- you might have to visit your Pediatrician once again. Hope my answer helps you. Wish your daughter a speedy recovery.