I am with you - hold off on the custom until she is done growing. If you ever are curious how much a horse “grows” in their 4-6 y/o years, start to take wither tracings. Looks like yours is still rather muttony - the wither is usually the last thing to “pop” up in a growing WB. :yes:
I am riding my 4 y/o in an Ainsley - so no glamor necessary - but I had a fitter look at it first and okay it. I suspect when she fills out and her wither appears the Ainsley will no longer be a good fit.
Anatomically, your horse looks like a pretty common young WB. They tend to be round and flat until their withers grow (5+6 y/o).
Best photos are taken level, with you standing about 5ft+ back, straight on (position yourself where the stirrup bars are). Then, from the front, stand about 4ft in front of the horse’s leg - that photo is so you can see spine clearance and fit across the shoulder (which is hard to see in this photo).
I agree with the other poster, it seems this saddle is sitting a bit too far forward (or the flap + seat is too long, as it doesn’t look like you have much room to move back without resting on the last rib) – you want the saddle to end before the last rib, but also needs to have shoulder clearance and the tree points should be set right behind the shoulder. You can usually figure out where the tree points are by looking at the brand logo button.
Run your hand under the panels from front to back, and back again; you should feel even pressure from front to back of saddle - any uneven pressure (especially over stirrup bar) is an indication the saddle doesn’t fit or may need to be reflocked.
Put hands on the pommel and the cantle - does the saddle rock up and down if you try to wiggle it? Does it sit stable? Rocking usually means the tree might not be the right configuration (too wide) or padding may be uneven. Sometimes it can be fixed by reflocking, but usually not.
Stand back and eyeball the relation between pommel and cantle - is one higher than the other? From a preliminary glance, this looks a bit pommel low, which will place pressure across the shoulders. To tell, I usually look at the seat - to me it looks like the seat is downhill.
From the photos, I think this saddle is too wide… But you should be involving a (good) saddle fitter to help you find a saddle to work for your mare.