My 16 Year Old Daughter Suffers From Migraines, For Which

My 16 year old daughter suffers from migraines, for which she has seen a neurologist. The doctor has prescribed an imitrix type med to treat. For the last month or so she has had radiating sharp pains that start at the base of her brain stem area and radiate up. last night she was complaining about dizziness. we are taking her back to her doctor tomorrow but of course as a mother if am very concerned. we want to ask for an MRI - concerned about a potential brain tumor. what is the likelihood and what else could this possible be?