If it is still paining off and on - it means the disease is still active or gets activated every time she restarts her activity / exercises. I would advise her to give complete rest from strenuous exercises till the pain is completely gone for at least one week. Then she can gradually start going for a walk to strengthen the muscles around the knee. Also, if she has gained weight recently a little weight loss may be very beneficial - more stress on diet control and less on exercise. Once she is able to walk comfortably for at least 4-5 km without pain she can try going on for aerobics and zumba. She can take Vit D and Calcium - best to consult a doctor in person for that.