It is difficult to determine the cause of jaundice in your wife from the data that you have provided. There are essentially three causes of jaundice:
1. Haemolysis - destruction of red blood cells
2. Liver disease
3. Obstruction of bile ducts.
It is usually possible to determine the exact cause by performing blood tests and screening studies such as ultrasound. Since her ultrasound is normal and only the indirect bilirubin is high, it is possible that she has haemolysis. You should consult a competent liver specialist who will be able to make the correct diagnosis.