You can't test for M.S. It's an illness of exclusion, so the tests that she's had have been for other illnesses. The manner of diagnosis is to undergo three MRI scan - brain, thoracic and cervical. If lesions are found in those scans, a doctor may request a "spinal tap." At this point, the doctor is looking for active signs of inflammation in the spinal cord. Concurrently, the doctor will order a battery of blood tests, which check for general health - nutrient levels, as extremely low levels of Vitamin D may cause symptoms commonly associated with M.S. - as well as thyroid issues, and potential autoimmune disorders (Lymes Disease, Lupus) and various cancers + tumors.
In order to receive a positive M.S. diagnosis, you need to show inflammation in the spinal cord, lesions in the brain and spinal cord and at least two episodes of symptoms.