Being on Coumadin, a blood thinner, does not help, but because of her heart condition is probably a must. It could be a situation where you are damned if you do and damned if you don't take Coumadin. The vessels in your mother's brain as the nerves could have been affected by her control of her diabetes. This is strictly a medical decision, and the course of action can only be done by doctors that have examined and tested your mother. No one, not even a doctor who might reply, can give any type of reliable diagnosis without examining and knowing the results of tests run on your mother.
Diabetics are much slower to heal that someone without diabetes.
The fluid on her lungs may or may not be related to her heart disease. Have her doctors mentioned congestive heart failure. This is one reason for fluid on the lungs usually because of loss of pumping action of the heart called the ejection fraction. To sum up, most of your mother's problems can probably be traced to her control of her diabetes. I am not a doctor, but I have been trained to do support work for heart patients and their families.