Usually, rapid eye blinking is resulted from eye irritation caused by dust, bright light, smoke, or foreign objects in the eye. Other reasons such as dry eye, allergies, or infections may increase the rate of blinking. You can tell her that she had this kind of symptom and suggest her to see an eye doctor immediately.
I know that stress, fatigue, or anxiety may lead to rapid eye blinking. But there is also habitual repetitive blinking. If she is too tired recently, you can suggest her to have a good sleep and relax herself. But if her symptom was result from some disease such as congenital glaucoma, it will cause rapid eye blinking too though it is a rare case in our life. I think this kind of disease will need professional suggestions and medical treatment.