Since AD/HD and seizures both require a medical diagnosis, suggest that your granddaughter's parents start with their pediatrician. He or she can do some screening in the office, but may also want to send your granddaughter to a neurologist for additional testing. The doctor will probably also want both your granddaughter's parents and the teacher to complete some behavior checklists and other information.
You may also want to suggest that the school counselor be asked to go into the classroom to observe your granddaughter. In this way, her parents could get an objective opinion of what may be going on there.