I can respect your concern. In normal course, there will be no issues with your married life. You mentioned that the girl did not have any seizure ever since year 12 years of age; I presume she is still under medication. Doctor's recommendation of proper sleep (uninterrupted sleep of atleast 7 hours will be good enough). There are atleast 4 or 5 different medicines for epilepsy depending on the intensity of the ailment.
Next Steps
Best suggestion is to talk to the girl directly (if you both are comfortable to do so) and consult her doctor/physician and discuss further. Once married and if she conceives, the feutus should be safe, healthy enough.