I worked at a mid-sized TV news station for a couple of years. At that time (2008-10) even the 11:30 show had a camera man who would have cued this person that they were about to be back live. The cue is given to the cameraman by the director watching in the booth; if they failed to tell the cameraman that they needed to cue the talent, something like this could happen. It would be rare though because the director has to tell the board operator to switch to the floor camera and the cameraman would hear this direction in his headphones (unless the director is running the board himself)…
Around the time I left that station there was talk about smaller stations being fully automated: the on-screen talent would program the entire show beforehand, and then would sit in front of the camera as it automatically ran through the whole thing… I’ll bet this is what happened here… She was all alone in the studio and no one was there to cue her that they were coming back to the studio camera… The perils of automation!
