She was shot with a pistol by a guy in a suit from inside the chambers. Possibly secret service or private security guard.
It sees that the capitol police officers actually moved in to cover her in what appeared to be a protective fashion after she was shot.
If so, apologies to the Capitol police
They had the chamber barricaded by some big piece of furniture. The window had already been broken. She was standing in front of the door peering in, and a shot rang out. The video shows her falling backward, and the people trying to help her, were having a problem finding a wound. She was bleeding from her nose, and possibly her mouth.