Our Adult Daughter Now 58 Had A Grande Mal Seizure

Our adult daughter now 58 had a grande mal seizure at the age of 18 when she was placed on Mebaral. She had been diagnosed with the ataxic form of cerebral palsy with mild spasticity soon after birth. She is mobile. When mebaral was discontinued several years ago, she was placed on phenobarbital, 32.4 mg, one tablet in the morning and two tablets in the evening. I am concerned whether this dosage is too high as she grows older. She has had no known seizures since the one at age 18. She is mildly cognitively challenged.