What Causes Headache & Nausea?

yes my daughter was playing outside today. i had her take breaks and drink water to keep her hydrated, she now complains of a headache and recently vomited. i got her some gatorade to re hydrate her and she seems to be feeling better. should i go ahead and take her to the emergency room? i am now feeding her some french fries for more salt intake.. am i doing something wrong or should i go ahead and take her to the emergency room?