Hi there and welcome to Just answer!! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
This red eye tells us that there is blood in the anterior chamber of her eye, This could be due to trauma or it could be due to a primary issue in the eye such as a tumor. This is common in cats Miss Sweetie's age.
Your vet will have to examine this and perhaps send you to an Opthamologist that can run further tests to determine which is causing this problem and then initiate the proper treatment.
For now, Apply a few drops of Artificial Tears to their eye every 8 hrs to soothe this area and keep it from getting worse. This can be purchased at the pharmacy over the counter.
Sincerely XXXXX XXXXX Loretta