Never tell police you are recording them
Almost all police vehicles have cameras....so they already consent to be recorded
Also, if so close to hospital, their cameras should also be recording
I expect her rationale was that if she told them they were being recorded, they would have pangs of conscience and stop beating the man brutally.
She failed to consider that if they do not fear their actions being recorded by a righteous and holy God, they will certainly not fear them being recorded by one of His creatures.