Does her saddle fit her well?
Has she ever gotten rubbed by the girth?
Are you cinching her up slowly, or yanking on it? And/or only cinching her up "snug" first, and then tightening it the rest of the way before you are ready to ride, after you've hand walked her a few steps?
I always look to MY behavior first to make sure I am not doing something to cause discomfort (which I why I kind of ask "how" you are cinching her up). And of course we always want to make sure this is a true behavior problem, and not her acting out because something hurts somewhere.
After you can rule both of those things out, THEN you can look at how to fix a strictly behavioral issue.
Personally, I don't have a problem with a horse pinning their ears while being saddled, if that's the only thing they do. Some horses are girthy so I just do the best I can from my end to not jerk the cinch as I am tightening it. I also will wait to tighten it fully until I have hand walked them around a little bit to relax them, before I'm ready to ride.
However, I agree that she should NOT be turning her head toward you and thinking about if she is going to bite.
Another tactic you can try, since smacking her nose once doesn't seem to do the trick, is that you can give her unwanted excessive attention. As you are cinching her, every time she start to turn and look at you, quit cinching and go to rubbing her head and nose excessively. We want this to be to the point where you rubbing and scratching her head and face is much, much more annoying to her than if she stood quietly and allowed you to cinch her up.
Of course, be very careful that you do not get bitten if she is threatening to do so. If she does indeed go for the bite, that deserves one HARD smack to the nose to "bite her back". Then go back to cinching. But if she is not actually going to bite you (and just thinking about it instead), the annoying head rubbing/scratching might be enough to prevent her from even looking at you while you cinch her up. Again, I think it's totally fine if she pins her ears as long as she is not looking at you while she does so.
So just more or less something else you can give a try. Of course, whatever you do, make sure it is 100% consistent all the time. If that means you have to pay attention 200% to her while saddling, then that's what you'll have to do.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.