I have a treeless and love it, but if you're a H/J rider, then you're out of luck. There are only a couple of treeless saddles out there that are made for jumping, and even fewer that look traditional enough to show hunters in. If you're an eventer or Dressage rider, then you can look in to Sensation, Freeform, Ansur, or Heather Moffett saddles. All make nice English models that are traditional enough for Dressage or Eventing.
If you want to stick with a treed saddle, then I would go with either a Courbette with their Swiss E-Motion tree (which self-adjusts to fit a few different shapes of horses), or something with a changable gullet system, like Collegiate, Wintec, Bates, Anky, Pessoa, etc.
Kevin, I agree that she shouldn't buy a saddle to fit a horse that's not hers, but it is important to have a well fitting saddle. English saddles are NOT the type to fit many different shapes of horses. If she buys a fixed-tree saddle now and ends up leasing or buying a horse that doesn't fit it, then she's stuck losing money on the saddle.
Well, actually, there aren't many fixed tree saddles out there that fit a lot of different shaped horses, western or english. With western saddles, you can find one that fits lots of horses because, well, many western horses are the same basic shape. Most western riders ride some kind of stock horse or stock horse cross. English horses can varry from small, fine boned Arabs, to tall lean & lanky TBs, to HUGE wide Warmbloods or draft crosses.
Different shaped horses require different shaped saddles/trees. Try putting your stock horse western saddle on a tall Thoroughbred or a small Arabian. Not gonna happen, lol.