My girlfriend lives alone in a hotel, and someone swipes her door with a card at night. Fortunately, her room was locked and the door was not opened. Why does that man have her room?

This must be done by someone inside the hotel. They can make a business card, which may be related to the night shift. But whoever opens the door with a card can ask the hotel to give an explanation, because the hotel has the obligation to maintain the safety of its guests. If this happens, the hotel must give an explanation and ask them why someone will use your girlfriend's room card to open the door.