Were the coworkers investigated? When she left work for her lunch break and came back to the building she was murdered in the parking lot. Considering she was murdered the moment she returned from her break makes me think that the murderer knew her. If she had a severe issue with someone close to her in the past that could help narrow it down. Was the car damaged in anyway?
Was there any cameras outside her place of work? Who else was on the same break time as her and were they questioned on their whereabouts during lunch time? Was anything stolen?
What was the cause of death? It sounds like this crime was committed on the spot, with no thought of who she was, just the idea to rob a car and go, but it ended wrong. Was the vehicle swabbed for the fingerprints, sweat, and blood of the perpetrator(s)? Were there signs of a struggle on her body? Signs of struggle in the car? I feel that the case details need more evidence so we can try to better deter this crime.
I wonder where she went for lunch and if there are cameras? Is it possible she was followed from wherever she went? Where was the place of work? Were there other vehicles in the lot? Were all cameras in the area checked?