I agree with most of what you have said Elana. She definitely wouldn't make a high end dressage horse for trouble getting her hindquarters under her but she would probably sit pretty enough to get around low level stuff.
One thing I am finding interesting is how different peoples perception is on conformation and what is right and wrong. For example, you consider this mare as being light in the bone and yet here in Australia it's become quite common for people to breed 'lighter bone, longer legs' on horses to increase 'prettiness' if that's a word in the show horse ring. If a horse measures over 8 inches of bone it goes in the hunter ring as its to 'heavy' for the show horse/hack ring. This mares bone wouldn't only be considered seen in the hack ring but considered normal. I guess it really comes down to the end result of what you plan to do with the horse and what breed it is to know what is truely a fault and what is just a different type.
Anyway, that's way off the hind end structure on this mare. Just something I have enjoyed noticing and proving that beauty is in the eye of the beholder!