First of all make sure she is not taking any sort of alcoholic beverages, because that can produce a "fatty liver" as well. If she does not drink then she needs to lose weight, and the way to achieve is very dependent on the person, but should include a combination of diet and exercise.
Exercise recommendations are at least 30 minutes of cardiovascular exercise (walking, jogging, bicycle, elliptic, etc) 5 times a week.
Diet recommendations for fatty liver are basically to have a healthy diet, avoiding foods high in cholesterol
and fat (no fried food, no shrimp, lobster; drink fat free milk or products, etc).
There is no medication available to cure fatty liver disease.