Fluid in body

Please can someone help me as I am getting very worried. I guess this is too severe a condition for anyone else to relate to, never probably heard of it. Last Autumn my sister aged 62 had pancreatitis and was very ill. SHe has had so many blood tests , scans, Xrays,MRI scans, ECG, the lot and no disease or tumours have been found anywhere in her body. All the liver function tests and everything are ok too. She had a very severe bout of flu in January and since she began her recovery fliud has ben built up in her abdomen and throughout her legs, which are very painful. She is only 5 feet tall and now weighs 6 stone.The consultant says she is suffering from malnutrition yet she does eat. She is under the care of three different consultants having had to see one privately.She is so sad and depressed and I am going insane with worry. Please someone tll me something! Thank you.