First and foremost we cannot diagnosis a potential disease process through described symptoms alone. It is important for your sister to visit a healthcare professional where medical testing can be performed such as, lab tests, chest x-rays, and physical assessment. Although her symptoms of extremity swelling, shortness of breath and fatigue are associated with fluid congestion in heart failure patients, they can also be associated with other diseases.  I am sorry we cannot give further advice but the social support you provide your sister will go a long way once a proper diagnosis has been made.