Seems like it pretty much has all been said. There are many reasons for headaches, including heat, abrupt changes in temperature, certain foods like chocolate/sugars, sodas, and foods that have nitrates, lack of sleep, tight hairstyles, allergies, sinus infections, jaw problems, neck muscle spasms...so I would stay away from those foods, keep her cool, take plenty of fluids,and have her see her pediatrician. Things to worry about would be constant headache that is worsening or that she wakes up to every morning, vision changes, instability, nausea/vomitting/dizziness, changes in behavior, seizures, weakness, especially if it is localized. Most pediatricians will advice these changes and a headache diary for a few weeks, to try to find out what triggers them, how often and severe they are, what makes them better, how ofter do you have to give tylenol/motrin, etc. Most insurances will not authorize an MRI right out, though it is the test of choice and doesn't have the exposure to radiation that a CT scan. So most people get the CT scan first, and in some cases it may take from a few days to a couple of weeks to be authorized, depending on your insurance and how diligent your doctor's office is in pushing for it. On the other hand, if there is somethig truly wrong or suspicious, then the plan would be to have her admitted and do a full workup including the MRI, but I'm sure that's not the case. Hope she feels beter soon.