Among the possible reasons are high blood pressure, coronary artery disease, and heart valve abnormalities. Discuss your mother's condition with her doctor, who should be able to suggest ways to help her. Diet and exercise and reducing her intake of sodium will probably be first and foremost. Sodium promotes retention of excess fluid, which puts a greater load on the heart's pumping mechanism. Eliminating added salt in cooking is also a good idea.
Salt substitutes are permissible and can make food more palatable.
Frozen and fast foods, which are notorious for containing unhealthy amounts of salt, should be avoided. Ask the doctor if your mother should restrict her water intake. In severe cases, this may be necessary to limit fluid buildup and swelling. Exercise can reduce symptoms and improve endurance. Your mother's doctor might suggest that she start a supervised, hospital-based exercise program designed for heart patients.