Rosemary Willis started to look away from the Presidential limo back towards the Texas School Book Depository at Z-140.
You are imagining something that is not apparent in the zfilm. She comes out of the shadow and her head does not turn. Here is z138 to z152 in slow motion:

At z145-152 her hood is pointing directly sideways so she is facing the President's car:

Rosemary Willis is marked no. 50 in the Tyler animation. If she was looking at Clint Hill, her head would be turned more than 90 degrees to Zapruder's line of sight and her hood opening would not be visible. But we can see her hood opening so her hood is facing the President's car. We can't see her face.
JFK began quickly turning his head to his left at Z-143.
Here is z140-151 in slow motion:

He does not move his head any perceptible amount. You are imagining this.
Nellie began a quick sweeping head turn to her right at Z-144.
She turns from looking forward, perhaps a little left, to looking forward, a little to the right. Not really quick or sweeping.
Regarding the former, JFK's last (as in final) wave began around Z-173, right before he passed behind the Stemmons Freeway sign and was hit in the lower neck/upper back by Oswald's second shot at Z-222.
Regarding the later, Chism and Woodward "recalled" this several hours, days, weeks, months, or years after the startling and traumatic event.
Chism gave his
statement on 22Nov63 within hours of the assassination.
Woodward went from Dealey Plaza to her office and immediately wrote the story that appeared in the Dallas Morning News the next day. She said:
- "The President was looking straight ahead and we were afraid we were afraid we would not get to see his face. But we started clapping and cheering and both he and Mrs. Kennedy turned, and smiled and waved, directly at us, it seemed. Jackie was wearing a beautiful pink suit with beret to match. Two of us, who had seen the President last during the final weeks of the 1960 campaign remarked how relaxed and robust he looked.
As it turned out, we were almost certainly the last faces he noticed in the crowd."
After acknowledging our cheers, he faced forward again and suddenly there was a horrible, ear-shattering noise coming from behind us and a little to the right."
Anyone with normal vision (evidently not you) can see that he lowers his hand over the next couple of frames until it's all the way back down at Z-150.
He moves his hand from vertical to horizontal. He does not move his head a perceptible amount. You are imagining this.