My Daughter Has An Infection On Her Knee. We Went

My daughter has an infection on her knee. We went to the pediatrician yesterday and she was given Bactrum. She took the first dose last night at 7pm and has now taken three doses. The site is still red, swollen and warm. She is complain of severe pain. We told her to wait two days for the antibiotics to have an effect and we've been giving her ibuprofen. She said the ibuprofen isn't helping and wants to go to the ER. We want her to wait another day for the antibiotics to have an effect. Is there anything else we can do for pain or should we go to the ER?