How do you know it is a migraine?

My daughter is 13.  She was told she exprienced migraines in 2005.  At that time she did not have head pain, just visual and stomach pain.  She did not experience any more symptoms or migraines until last year, March 2007.  She experienced head pain and at first was treated for sinus and them tenion headache.  She was finally admitted to the hospital and given DHE.  She did well and had no problems until Feb. 2008.  She began being treated for sinus, three rounds of antibotics and steroids.  The neurolgoist said it was migraine due to the sinuses.  The ENT said there was not problem with the sinuses.  They tried Frova, imatrix, relapax with no relief. She was put in the hospital again and given DHE.  The DHE lowered her pain but did not relieve it.  She has had a head ache since Feb.  They recently tried Inderal LA.  Her blood pressure dropped 83/50.  They discontinued it.  She is constently experiencing dizziness.  At first they said it was her first sign of a migraine and to give her the relapax.  If I give her a relapax every time she is dizzy, I would be giving them to her constantly.  They don't seem to have any effect.  She is tired a lot and her dizziness seems to be getting worse.  Could there be something we are missing?