Well, you asked...so I'll give what is probably an uniformed opinion:
1 - I don't like hooky necks and no withers. It seems to be the thing halter classes look for, but I'm a fan of withers and a real neck.
2 - I don't like her training - not for dressage, at least. And I'll admit I'm not a dressage fan or rider, so take this with a big sack of salt...but I saw a horse with no collection. Squished in head & neck? Yep. Driving force from the rear? Floating movement? Nope. Judging from the video, I think you would have to unteach her - train her to stop doing what someone has trained her to do. Only then would you be ready to start training her.
Of my 3 horses, one is a purebred Arabian mare & one is 3/4 Arabian & 1/4 Appy. I sold another purebred Arabian mare 14 months ago. None of them carry their head that high unless they are unhappy and hollow. I fully understand that Arabians have a high headset...but that is too high. IMHO. I only see that when they are getting resentful.
I think you would have to first teach her to relax her neck and back, and learn to drive with her rear. Attempts to teach her real collection would be a challenge because she has already been taught to squeeze her neck instead of shifting her weight to the rear.
Please take this with enormous skepticism. My mare is 15.3, and she wouldn't win anything in halter now - but I think it would be easier for her to learn dressage than the horse you are looking at. She can float when she wants to, although she normally prefers to stretch out and go. With my oldest daughter: