On a small narrow wither-having pony with a pointy top of the croup, you may not actually end up with any choice at all if you want even just-barely-adequate saddle fit
It is very easy to run into problems with the saddle rubbing the horse in the upwards slope of the back, or even atop the hindquarters, and that is a fast ticket to pony behavior problems and scared kids. You may need to find a *short* saddle (it's the panels or skirts that need to be short from front to back, which does
not necessarily relate to seat size, despite what logic might suggest).
Look at the wintec little-kids' saddles, even if you would have preferred a western saddle, they are cheapish and generally pretty useful, assuming you can get 'em to fit this pony (and I think your odds are better than with many other brands). Actually, I apologize for forgetting what age your daughter is, but if she is still pretty young you might even look at wintec's leadline saddle (well, that's what they used to call it, I have not chcked to see whther they still make it or if it's still called that), which is an awfully good starter saddle for the Very Young set, like up til they get to controlling the pony well at walk and trot and starting to canter independantly with a decent seat.
Of course, if you have a *choice* between saddles, then as others have said, DEFINITELY go for one that fits your daughter now. It is hard enough learning to ride, and dealing with an unfamiliar and possibly not 100% broke pony -- kids really don't need the extra complications of slopping around in a too-big saddle with the stirrups in the wrong place
Have fun,
Pat, who used to teach riding a long time ago