How Can Water Retention While Suffering From Diabetes Be Treated?

My sister, 58 years old and a smoker and with diabetes is experiencing significant water retention. She put on 30 plus pounds in the month of December alone. She is also experiencing high blood pressure. Her Dr. did some tests and determined that her urine contained a significant amount of protein. Kidney problems were suspected and a biopsy done. The biopsy showed that her right kidney was functioning fine, but her left kidney had lost 30% of it s functionality. She has been home for about two weeks and is awaiting further tests. In the meantime she has developed severe diarrhea that has lasted about 10 days and has informed me that once she eats anything, she has an episode of the diarrhea almost immediately. She tells me she has not been given any diagnosis for why all of these symptoms are occurring. What are the possible diagnosis? I am her older brother, living 1,000 miles away and concerned.