Suggest Treatment For Swelling &redness In Ankles

My sister in laws right leg below the knee to the ankle is red & purple in color very swollen, hot and tender to touch. She was in hospital for this she was told infection but they did not know what caused this situation. It is now almost two weeks later and now both legs are purple and look the same. Still has same symptoms and antibotics r not working. Any suggestions please she needs direction