You are trying to manufacture a justification for the murder of a mom because she was not free to leave and (you claim) assault. Neither of those are crimes punishable by death, nor allow for deadly force. And neither of those allow for extra-judicial enforcement of a punishment (murder).
She was killed because, in the words of the shooter, he considered her "a fucking bitch".
The car wasn't aimed at him, it was slowly turning away, it didn't hit or touch him, his hand held phone jolted as he fired. He was seemingly fit and unharmed as he stomped away angry after firing three shots.
He moved into firing position as he didn't want her to leave and wanted to shoot her to stop her.
