My Daughter Is 10. She Fell About A Week Ago

My daughter is 10. She fell about a week ago and scapped her knee really bad. Then last weekend she developed a rash (reddish brown in color about quarter size) on her lower area of neck, near hear line. We went to dermatologist yesterday and she said the knee was infected and has spread to her neck. they prescribed mupirocin 2% to use twice daily. She went to soccer practice tonight and called crying saying her head was throbbing near the rash area. She couldn't stand going over speed bumps on the way home or bend over. My husband recalled she also had a lower back pain come out of nowhere about two weeks ago that last about 3 hours. Not sure if that means anything. She is my "tough" girl so to call crying about this is very unusual. Do I need to worry and what could it be?