Eye problem. It be stable as it is now?

Hello sir/madam, My daughter is 10 years old. When was 8 years old she wore -2D spec in both her eyes. After 2 years the eye prescriptions were -3.25 sph ,-0.75cyl, 180axis nearly same in both eyes. Doctor examined the eye after installation of a drop in her eyes. Doctor said that his corrected vision is 6/6 in both her eyes. And do come after 6 months to recheck eyes. Now two days ago I met my my friend who is optician he checked my daughter and said that the corrected vision in her left eye is 6/9. And 6/6 in right. Is it possible to decrease the vision so rapidly or it is just a mis judged by my friend. If the digonisis is correct then wheather the eye vision decrease further or will it be stable as it is now? Is there any impact on right eye also. I am really worried about by daughter. What should I do , should I wait for another four months to recheck or just recheck now. Please reply sir. And thank you in advance.