Can you advise me about how to talk to my grandmother's doctor?

It's important for you to talk directly to your grandmother's physician and explain your concerns about the effectiveness of her current medication. It sounds as if you're hesitant to interfere with your grandmother's medical treatment, but you'll likely discover that the physician welcomes your feedback, as she may not realize that the medication is not working. Physicians rely on such information from patients and their families to make their diagnoses and treatment plans, and if you keep silent, you're preventing your grandmother from getting the best possible care. As long as you approach the physician with respect, she should be open to hearing what you have to say.