Hi, there are a number of causes for membranous nephropathy (MN). some are transient and some remain for life. Prognosis depends on what has caused it. Many viruses like Hepatitis, drugs, infections, connective tissue diseases can cause MN. once your nephrologist finds out the cause, appropriate treatment would be started. Generally, steroids are given which will offer some cure from disease irrespective of the cause. Cut her sodium to less than 6 gms/day to prevent edema; potassium rich foods are better avoided as there is accumulation possibility, but is generally followed by serum potassium levels. All the best.