Concussions are usually injuries no one sees and, contrary to popular belief, don't show up on most magnetic resonance imaging (MRI) exams or CT scans. As a result, conventional CT or MRI scans of the brain are usually not needed where post-concussion signs or symptoms are mild and clear within a week to ten days. Concussions are typically associated with grossly normal structural neuroimaging studies in general. Routine MRI is, however, recommended in the cases where 1. Loss of consciousness (LOC) for more than a minute seconds (concussions may or may not involve LOC, with 90% of all concussions occurring without LOC), 2. Prolonged impairment of the conscious state, especially if there is any suggestion of a deteriorating level of consciousness, 3. Dramatic worsening of a headache, 4. Speech or language difficulties such as aphasia or dysarthria, poor enunciation, poor understanding of speech, impaired writing, impaired ability to read or to understand writing, inability to name objects (anomia), 4. Vision changes such as reduced vision, decreased visual field, sudden vision loss, double vision (diplopia), 5. Neglect or inattention to the surroundings on one side of the body, 6. Loss of coordination, or loss of fine motor control (ability to perform complex movements), 7. One-sided eyelid drooping, lack of sweating on one side of the face, and sinking of one eye into the socket, 8. Poor gag reflex, swallowing difficulty, and frequent choking, 9. Seizures, 10. Worsening post-concussion signs or symptoms, or persistent symptom, longer than 7 to 10 days, like in the post-concussion syndrome.

A CT scan is the test of choice to evaluate for the four types of intracranial haemorrhage (subdural, epidural, intra-cerebral, or subarachnoid) bleeding in the brain, swelling of the brain during the first 24 to 48 hours after injury, or to detect a skull fracture because it is faster, more cost-effective, and easier to perform than an MRI.  No test, however, currently available is sensitive and specific enough to diagnose all intra-cranial injuries. MRI is viewed as superior in detecting traumatic lesions of the brain, and does not expose patients to radiation, its use is recommended for assessing traumatic sport-related brain injuries, especially after the acute period.

For more information: http://www.momsteam.com/health-safety/ct-or-mri-usually-normal-after-concussion-but-recommended-in-some-circumstances

As she was having persistent symptoms like headache, the MRIs are justifiable.