That's not necessarily correct. It depends on what it was (if anything) that prevented her from seeing the limo. It didn't have to be a wall.
I agree John. It's not "necessarily" the case.
The point I suppose I was making was that Altgens 6 strongly indicates that people stood on the east side of the steps have a clear line of sight to the limo during the initial part of the shooting at least.
It's true that, perhaps at the key moment a person could have sand blown in their eyes so it wasn't possible to see the limo or maybe a pigeon attacked their face making it impossible to see what was going on or maybe....lots of other unlikely possibilities.
But if they were just stood there watching, and nothing weird happened, and they were following the limo with their eyes, I don't see any realistic reason as to why they "couldn't" see what was going on.
Perhaps you have a more realistic suggestion as to why someone stood on the east side of the steps "couldn't" see the limo.