Beautiful, rounded hindquarters. Good length and curvature to her back, love how it flows right into her croup with no awkward breaks. Neck is lacking muscle but that could hopefully be helped with more riding. Great angle to the shoulder, I would imagine this gives her wonderful gaits. She looks nice and trim, with no sagging gut despite having had a foal, which means she is in touch with her belly muscles (so important for collection!).
Only cons I can see are that her front legs appear a little short, but perhaps it is just the camera angle, and also that her hind legs are somewhat camped out behind her, but they tend to stand that way when they're in heat so that could be why. Her croup is higher than her withers which may make it tricky to draw herself in and collect, but she is Spanish and they are legendary at dressage so I'm guessing it's not a problem. :)
I know she isn't your horse, so you may have no control over this other part but just want to throw in my observation :) :
Assuming she is a normal, healthy horse and not being treated for founder or anything of the like, I don't care for the way her feet are trimmed. All her toes look too short to me. Her front feet appear strained at the pastern joint, and all 4 pasterns look too upright (her hinds almost completely so).
Having her hooves this upright most likely shortens her strides (breakover point comes sooner), and I would be a little concerned that this would cause strain in the front pastern joints and/or bruising in the toes if she is ridden often or jumped. Not an issue for light flatwork, just something to keep in mind if you start jumping or purchase her, or if you're able to influence the farrier. :)
Hope that helps, and best of luck! She is a beautiful mare. Dapple grey is my absolute favorite coloring!