I have a thin friend with super long legs- like has a hard time finding a saddle that isn't huge in the seat or doesn't have her legs passing the flap long- and she has had a couple of HDR pros over the course of time. They're definitely not top of the line, but they're pretty good saddles, and aren't overly pricey for something that your daughter will outgrow. When I met my friend (at age 14) she had a 16" HDR pro with extra long flaps, and it fit her well at that time. I think it was a bit large when she got it, and by the time she sold it quite a few years had passed and she had outgrown it in both seat and flap length. She got another one after, but had to sell it when it didn't fit her horse. She's now back in the market, and while she is looking for something nicer than an HDR I do think that the only good fit I've seen on her as of late has been her most recent HDR
One thing that I have heard is that, like many saddle brands, the HDR pro has decreased in quality over the years. As such I would look into buying a used saddle that is at least a few years old rather than buying new. Plus, it's cheaper that way
All in all, I've enjoyed the limited experience that I've had with the saddles, and think that one will probably suit your needs. Get one that has a little growing room to it, and when she outgrows it you can either buy another intermediate saddle or one that will be more suited to her adult size, and perhaps upgrade to a nicer brand and sell the old one.