There are two things I would do before administering meds or taking her to the doctor:
1. Evaluate her diet very carefully and be sure it is mostly whole and natural foods. Avoid processed foods and snacks that can be high in sodium, MSG, artificial colors, flavors and preservatives. AVOID SODA and artificial sweeteners and opt for water or diluted juices (use seltzer water for the "fizz" and they won't miss the soda after long.) Children can be especially sensitive to these ingredients, as evidenced by behavioral, learning and chronic health issues. Go REAL with your food! If you need a great resource, please check out http://www.feingold.org/ for information on foods that can trigger issues like headaches as well as ways to find practical - and tasty! - alternatives.
"Let food be your medicine and your medicine be your food" ~Hippocrates
(...not that this means you should down a bottle of Advil for your dinner - ha!)
2. Consider taking her to a chiropractor. While most people associate chiropractic with back issues, ensuring that the body is in proper alignment boosts the immune system and can benefit children with headaches, bedwetting, ear infections and a host of other issues.
If you incorporate these changes, ride them out for 2-3 weeks and see if there is any improvement. If not, I would then consider taking her to the doctor.
I speak from experience here - as a child/young adult, I had CHRONIC, debilitating migraine headaches. Since I have followed this advice and changed my diet I have been mostly headache-free - with the exception of stress headaches, etc, which aren't the same at all. My DH, 1-yr old DS and I go to the chiro weekly - it's worth it if/when insurance can cover it for you.
Just a thought...allow a few days to go by without saying anything to her about it or asking her how she feels. By all means, if she approaches you with it, then acknowledge, but on the chance that she is allowing some drama to get your attention don't let on that you're worrying so much about this. In the meantime, perhaps consult the dr, make any necessary dietary changes and see what happens.
Good luck, mama!