My Daughter Went To The ER Yesterday Morning, Diagnosed With

My daughter went to the ER yesterday morning, diagnosed with MRSA. The redness was about the size of a tangerine, now its bigger, as evidenced by the photos and very very painful. She was prescribed Keflex and Bactrim. How long does it take the antibiotics to take affect? She has low grade fever presently and small amount of yellow discharge. . The area is on her abdomen, now has spread to around her side. Does she need to go back to the ER?