As your mother is diabetic and now suffering from diabetic myopathies. The edema or swelling of legs and feet is due to diabetes and also due to kidney failure. The renal failure is also due to the diabetes. For more information, visit Diabetes
Does Renal Failure Cause Excessive Retention Of Fluid?
The purpose of the kidneys are to filter negative particles from our bodies through urination. Some people can urinate large amounts, and do so frequently and have problems because the kidneys do not filter, so all the time it is not the problem of retaining water, but also cleansing. I am happy she is getting them filtered. I can see your caring heart, and if you trust your doctor, these days will be filled with knowing what a precious and caring child she has and even if she does not voice it, this is more than likely on her mind. I know her days are better just seeing your face. I worked in a Nursing Home and have seen families react. I wish you both the best, and you take an extra helping.
You could ask a doctor for a second opinion in her health and course of care ,i think you need to be aware your mothers age will be against her in this illness and that she sounds quite ill I'm sure you are doing your very best to help and I'm sure she knows this too take care