too much magnesium causing migraines

That sounds ridiculous. My doctor (a headache specialist) instructed me to take magnesium twice a day, everyday. The only side effect I have ever had from taking too much is some diarrhea. Why take synthetic medication when you can improve your heath with things that are natural. I'm glad you are having success with the topamax. It never worked for me. Just pay attention to your mood swings and other side effects - those can get bad.

I have just started my 6 year old on manesium supplements for migraine as his is accompanied by severve cramping in the legs and feet. 

I'm so glad to hear you are feeling better. It is such a great feeling when we are not in constant pain.

As far as your niece goes, when taking any supplements it should always be discussed with the doctor. Having said that Magnesium is a fairly effective preventive for some people, and some of those people haven't had allergy testing before they started it, I know I didn't.

Has she seen our Migraine medication prevention list? Near the end of it supplements are listed. Coenzyme Q10, Vitamin B2, and Petadolex are also effective for some Migraineurs. A word of caution: these are "natural" supplements being used and will still interact with our bodies as drugs do. Care needs to be taken when we use them.  Let me know if you need more information, ok?

I had been using Amerge (a triptan) which worked for fixing my migraine, but wanted to prevent them and tried many of the natural supplements, including some of those mentioned in others' comments.  None of them worked for me or I had side effects with no relief.  I did go to an allergist, but mine didn't test for other things like food. I mentioned that I got migraines from drinking alchohol, but he dismissed it as something that can cause headaches/migraine, but that it wasn't a true allergy.  In the end, it was food with gluten (items made with flour from wheat, rye, barley, oats) that causes my migraines and he hadn't tested for it.  For free, your niece can follow a restrictive diet and add foods back into her diet to see if something triggers a headache/migraine.  I didn't get a migraine every time I had a gluten item, only in combination with my female  cycle.  It meant that I had the migraines once or twice during the month and then a week before my cycle started.  Some of those headaches can be 2 or 3-day headaches.  I'm sure there is info on the internet about restricting food items that might help her to determine if it's a food thing.  Usually it incorporates keeping a food diary.  Such a headache doesn't always happen within an hour, but can take up to 4-5 hours for me.  That's why a food diary alone may not be helpful, but combined with a restrictive diet might turn up something.