Recurrent headaches also fall into that category of nonspecific complaints like bellyache, chest pain, or other possibly psychosomatic symptoms, where the body may be responding to a particularly stressful situation. Stresses in a family such as marital problems, family separation, or divorce are factors that have been associated with recurrent headaches in adolescents.
I suspect that your daughter's normal MRI was somewhat reassuring to you. Many parents often want to first know that the recurrent headaches are not due to anything "serious." Yet she is still complaining, so now what? I'd recommend further exploration of your daughter's headaches. Discuss this with her doctor. Specific questions can be asked and a thorough examination can be performed to perhaps better pinpoint the cause(s).
Occasionally, a phenomenon of rebound headaches with regular, frequent use of pain relief medicines like Motrin has been the unexpected cause. If her headaches are very debilitating to her, it might even be helpful to have her evaluated by a neurologist.
Once an underlying cause is identified, management can be more focused. Reassurance and education should be included as cornerstones of treatment. For example, with tension headaches, medications are not always the answer -- rest and learning to cope with a stressor can be more effective. Medication use should be thoroughly explained to you and your daughter. It is important to know when and how each medicine is to be used and which triggers, if any, can be minimized or avoided.