My daughter was punched in the back but no one was there. What could it be?

My daughter was punched in the back and it left a red mark. No one was in the room with her. She screamed for i ran upstairs and looked at her back, it looked like someone punched her really hard. I brought her downstairs, and as soon as she got downstairs the pain was fading as well as the red mark. She had went to a cemetary and took pictures. Dont know if that has anything to do with it. Have'nt slept in the room since. I want to know what i can do to get rid of it.