Yes, try the different saddle, this one doesn't fit at all. What it looks like to me is that the gullet is too narrow, causing the saddle to perch up on the very top of her back, and the bars are too flat, causing them to only have contact at the very top and the bottoms are angling out away from her body. I can only suspect about the bar angle as the one picture from the back seems to show that the saddle is flatter than the angle of her body would match. However, the picture from the side pretty much solidifies that the gullet is too narrow. Look at the conchos at the swells of the saddle, they are above the level of the withers, which means that the top part of the bar is pinched together right up on the very top of her back by her spine.
While she does appear to be a very wide horse, her back is not broad and flat the way that a thick built QH is. You may have a bit of trouble finding a saddle to fit her. Do you know the measurements on the saddle you're using now for the gullet width and bar angle?
Also, the fact that the cinch and latigo is at such an extreme angle up to the rigging is a big clue that the saddle isn't right for her.
Just as a comparison, here is the side pic that you posted; see how high the conchos are and the angle of the latigo. Also look a the back of the saddle, see how far it sits back on her hindquarters and how high it's popped up off her back? That saddle just looks like it would slide off if any type of pressure was applied in any direction.
And here is a well fitting saddle. Notice how much lower the conchos sit on mine, but there is still adequate room between the withers and the bottom of the gullet...and the cinch is in a relatively straight line from the very bottom all the way up to the rigging. Also notice how the saddle sits down on the horse, the back doesn't pop up the way it does on yours. If the saddle fits well and the person is a good mounter, then they should be able to step on without a cinch on a saddle at all.