Florrie had finished dropping off a patient at A&E and was in the reception area chatting with one of her friends on the Welcome staff when the Dark Mark appeared. While she herself wasn't injured, she was shaken and frightened, and had to help the staff corral and deal with injured patients and waiting folk.
Everything seemed to be settled with injured people (all minor) after about an hour. Fortunately for Florrie, injuries were her biggest problem and since she was on premises, she was seconded to deal with them. This meant that by the time the injuries were settled, she had a decent idea of where the Mark had been seen and roughly the path it had taken to get to the visitors' cafe (up the main stairwell). Which was when she moved to report about it.