This is more a matter of police training and procedure. Presumably, they teach something at the police academy before they give them guns and badges - and she was accompanied by a male partner.
The whole operation seemed kind of amateurish. In the video, you will see a male officer without body armor and without cover firing a handgun at the trailer from about 30 feet, when he knows the guy inside has a shotgun. Then he is shot.
This incident will likely become a lesson in police academies around the country under the heading of “Don’t Let This Happen To You.”