Oh man….
This is like asking us for a good place to buy boots.
I'd suggest you buy used for two reasons…you'll get way more quality for your dollar and…she's going to outgrow it.
Next question….what kind of riding? My kids do ranch work, barrels, western, English….every saddle is different. I dont know how many saddles we bought since they started.
So why don't we start with her size and what she wants to start working on.
After that, we need to know a little about the horse to get the right fit on the animal.
For my dollar….my circle Y "all around roping" are really nice and they won't break the bank. I have a couple of very nice saddles that are from local makers. You really need to kind of learn a little about saddles so you can make a good decision on this.
You should be able to find a very nice saddle for 400-600 dollars. I would highly reccomend buying local and setting up a deal that you can back out of. I've never had anyone not allow me to buy and try a saddle for fit of the horse and rider if I'm not sure and they aren't willing to refund, they can find another buyer. After you buy 15-20 of them you'll know what she needs as she needs it.
Sorry for so many words but it's not quite as simple as it seems.
It's nice that's you're doing this. Support for what she's doing is awesome. It's a lot of fun but it only gets more expensive from here.