From the pictures, it looks like it fits her good. Your saddle does not look 'perched' which would be a sign of it being too narrow and it is sitting pretty level so that is sign it is not too wide. It is not too long for her back and overall looks good. Your new longer girth would be good for her comfort and your stability.
As far as wither clearance, as long as when you are sitting in the saddle, there is no pressure on the withers when you are sitting in the saddle, I would say it is not too wide.
Basically, 'air is air' , so if it is not touching her withers when you are riding, 2 inches clearance or 4 inches clearance is the same thing.
In general, a thicker pad makes your saddle fit a bit narrower, a thinner pad makes your saddle fit a bit wider.
You can see the saddle in my profile pic is too long for my horse, so I have to put it up too high on him thus limiting the movement in his shoulders and it is a bit too narrow, so it does not sit level.
His dressage saddle however, which is an xxwide fits him (and me with a 36" inseam!) perfectly all around in wither, back & shoulder: