What Causes Swelling And Numbness On Left Knee After Knocking?

3 weeks ago, teen took a bad double bang at the skate rink. Another skater fell on and stomped on her left kneecap and then knocked her onto the hardwood floor, thereby hitting the left kneecap again. Went to E.R., she was given meds and told to rest and take it easy and use crutches for a few days and it should get better gradually. It seemed to. She was reinjured by a friend knocking her over this evening and the knee has swollen back up and is again numb. Wondering if we should go to E.R. again or should we wait for Monday to see a knee specialist or what?