Hi, Thanks for writing in. I suppose she has been given required first aid and also taken tetanus shot, antibiotics and pain killers. The swelling needs to be seen before recommending a X ray, however I do not think a hairline fracture would have occurred as she is bending her knee and a fracture usually is very painful and accompanied by persistent swelling. Most likely she has sustained soft tissue injury and that could mean tendons and ligaments too. There are many structures in the knee joint apart from bones and everything cannot be assessed by X ray. You may wait another week for the wound to heal completely and restrict her physical activities to minimize the pain.