Thank you for your question. My name is***** I have been a small animal veterinarian for 14 years and I'd like to help with your question.
Many dogs with diabetes develop cataracts. And it seems like the older they are when they are diagnosed, the more quickly the cataracts develops. Unfortunately, the only treatment for cataracts is surgery. There are no medications or drops that help. There are drops out there that reduce inflammation in the eye. A lot of dogs with cataracts will have inflammation in their eyes so these drops can help with eye discomfort. However, they will not help with her vision. I'm sorry there isn't a better answer. I understand that at 13 it would be a huge undertaking to do surgery on her. It is a difficult position to be in. Let me know if you have more questions and I will be glad to help. If not please rate my answer. Best wishes!
So.... if the eyes are red or if she blinks frequently like they hurt, there is probably inflammation. But the best way to tell is with a slit lamp to look at the eye... which only an ophthalmologist would have.