Why would she sincerely do a salute like that? What's to gain? The vote of white supremacists? I'm pretty sure they already got those locked.
But they think they can win by engaging all the closet racists and white supremacists. They think there is a huge groundswell of support waiting to be tapped if they can indicate that yes, they know what white America wants and they will deliver that.
It was absolutely intentional. Is Ingraham a Nazi? Not literally, although her professed political beliefs skew pretty close much of the time. This is physical dogwhistling. She's either making the gesture intentionally, knowing people who agree with her will get the wink and people who disagree who point it out can be deflected with a simple "A Nazi salute at an American political rally? That's
crazy talk!" routine. But the video is very clear. Nobody waves like that.
And no, none of the still shots of Hillary look like a Nazi salute, and if you watch those shots in motion, they're just screen grabs of a normal wave action. What Ingraham did was very, very distinct. This woman is Ann Coulter 2.0, basically. She knew what she was doing.