A fast-food restaurant clerk was shot in the back as she tried to flee from an armed robber, authorities reported. Mashi Nyssen of Los Angeles was listed in serious but stable condition at County-USC Medical Center. Sgt. Paul Hermann of the Los Angeles Police Department's Northeast Division said a man walked through the back door of a McDonald's in the Highland Park area, brandishing a revolver with a six-inch barrel. Nyssen, 19, one of three employees readying the store for opening, was shot in the lower back as she tried to run out the door, Hermann said. The gunman robbed the store of an undetermined amount of cash before fleeing, police said.