What Causes Huge Rash Between Thigh Joints?

My daughter 20 years old has developed a huge rash in between her thigh joints. Skin specialist at St. John's has prescribed ointment saying it is only a fungal infection and it will be cured in three weeks. But even after a week nothing seems to have changed. So can you suggest whom to contact now? We live in Koramangala, Bangalore.