Well her colour is really quite nice!
I think she's probably a little thick through the jaw, her neck is of adequate length and it ties in well to her chest. She has a high wither, but a good back. Her shoulder is quite nice, but I am undecided about her knees. I can't decide if she is a touch back at the knee, or just right. I think her pasterns are a little... Off. There is just something there in both pictures I don't like about those front pasterns. She is built uphill... Good for dressage. Her hind end, in all honesty, is her worst feature. In your avatar, especially, you can really see that she does not have that rounded apple rump you want for power in the dressage ring. I would have her checked out by a chiropractor actually, then when your in the clear, start strapping her hind quarters (only if she tolerates it). I find strapping is really helpful. Also hill work will help her muscle up there. She will never have that apple shaped bum, but muscling up will improve it a lot. I think she has quite weak gaskins, moving down into sickle hocks. She has a well set tail and a nice enough top line. The top line could be better, but loads of long and low will help her there.
Over all I think she's a really nice mare, and I wish you the best of luck pursuing your dressage career!