To me it looks like it sits low in the front and that is why there is a gap in the back. In the second picture (side view) of the saddle, the seat isn't level and dips forward in the front. If a saddle is too wide it will sit low in the front and actually pinch the withers.
This could also be caused by the saddle being too far forward. How to position the saddle on your horse: Proper Placement
Looks too wide as measured horizontally to me. The angle looks OK, so I would pad the front part of the saddle. I think the easiest way to do it is to fold a small pony wool pad and place it in the front.
I think the fit is not bad. I agree with bsms that it might be a bit wide and need padding up (with a pad that has wither cut out ). The angle looks about right. If she has ridden well in it so far, I would accept it as good enough.