Thanks, Tinyliny! I asked her and she says that some of the time she rides in a different saddle, which was the trainer's when she was a child, so I assume at least some of the time she has a better fit with the saddle.
About the flapping--is it the saddle's fit, or the way it was put on?
What makes you say that she's more suited to English riding? She wants to ride Western for now, and I find that the barn culture is much nicer in this barn than in the English barns here.
What would you suggest she do with her arms instead of pulling them back? Why is she instructed to pull back? Why it is not a good thing?
I'm a little confused as to why her instructor has her posting then....as posting is not a western thing. Although...I WILL long trot my WP horses and post, but for western...she needs to learn to sit a jog.
She is in a chair seat, as her thighs are up...she's not stretched down through her whole leg, and she needs to bring her leg back at he hip. Her thighs should be pointing more toward the ground.
This is me on my WP horse I retired two years ago, and even in this pic....I could bring my leg back a tad more from the hip:
See how my hip to knee, then knee to foot is almost the same distance? This is what you want western, it's very close to a dressage leg.
Your daughter is cute as a button and love her upper body how straight and quiet it is. But if she wants to ride western, she needs to learn to sit the jog and not post. Many times that is the rider's downfall....not being able to sit a jog and sit it correctly.