I was going to say... she looks like a young mare who has need of a conditioning program. I'm also thinking she could be stood up a little better.
Based on this photo...
She has a nice sized head for her build, a rather straight neck with upside-down muscling. I do like how she ties into her chest, and it is a nice deep chest (no front shot to see if it's also a nice wide chest).
I actually find her shoulder slope LOOKS steep (again, I need to grab a protractor for this computer... then we could all see), though it does have length... and it is paired with a decent shoulder angle.
I won't comment on her front legs - ideally they wouldn't be booted for a critique, so in light of the fact she is, I just won't comment as it's impossible to see well.
She does have a good amount of heart-girth, and while she's lacking topline at the moment, I think we'd see a better join with her wither.
She is wasp-waisted (or rather, she's lacking in loin-girth depth)... this isn't a good thing as we want to see a nice deep loin-girth to help support the back from the hindquarter. Based on this photo, it also looks as though her loin is on the long side - even though she has a short back. This will also hinder her ability to have a really strong back.
From the look of this one photo, her LS placement is pretty good ("good" being in line with the point of hip... "ideal" being just in front of the point of hip... "poor" would be anything behind the hip). The LS is important because it is the rear "anchor" for the spine - and it plays an important part in how easily the horse can change gears (be it gait changes or turns)
She is pretty downhill... but as a 4yr old, she may yet even out a bit. I doubt this little mare will ever be uphill though, and that will also make it difficult for her to shift her weight back and lift the forehand.
Her hip length is pretty good, but the hindquarter as a whole doesn't appear to create that ideal equilateral triangle.
She's not standing well behind, but, I'm going to guess that her hind limbs are OK as far as angulation goes.
Overall, this little mare lacks balance... she has some strong points, and she has some weak points, and right now, I'd guess that those weak points are what are standing in the way of her working correctly. It's going to take a lot of work to get this horse moving correctly, and a constant struggle to keep her there, though I don't see that she will have any actual soundness issues due to her conformation.
Bear in mind, that when judging a horse based on photos there is some distortion from the lens, we're dealing with a horse who's not standing quite correctly either... these things can change how a horse looks pretty radically.