Why would that be necessary in order to look away from the limo and back in the general direction of the TSBD?
She is running and her shoulders are square to the direction she is running. So if her head is turned 90 degrees, her face is looking straight across Elm St. and that would be right at the limo. Here is Tyler's animation at z144.3 which is the closest I could get to z145:

I have no idea how to tell whether she is looking at the TSBD, the car, the road, the sidewalk across the street, or something else. All I can say is that her hood is turned to the right about 90 degrees to her shoulders and the President's car is directly in the sightline if she was looking in the direction her hood is facing. I don't know why she would not be looking at the occupants of the President's car.
Some witnesses said it sounded muffled (which makes sense given the fact that it was a steeply-downward-angled shot which required Oswald's having the muzzle of his short-rifle inside the building).
Since the occupants of the VP car said that their car had completed the turn and was going toward the Triple Overpass, and since the VP Security car occupants said that they were just about to complete the turn onto Elm (eg. "We turned off of Houston Street onto Elm
Street and that was when I heard the first shot" -Joe Rich 18H800; "our car had just made the left-hand turn from Houston onto Elm St. and was right along side the Texas School Book Depository" - Clifton Carter 7H474), and since Croft said the the first shot was after his z161 photo and Betzner said it was after his z186 photo, and Mary Woodward said it was after JFK began his last wave as they passed by where she was standing (at the lamp post opposite JFK at about z192), ALL OF THESE PEOPLE would have to be COMPLETELY MISTAKEN IN THE SAME WAY but for different reasons. What could have caused that? How can that possibly happen?
Why did she snap her head to her left and finally start looking at the limo around Z-214?
She had seen the pigeons fly from the roof of the TSBD by then. Why would she continue looking at the TSBD? Another look toward the President doesn't seem unreasonable.