Gee, there's a LOT to like about this filly. From the way you were talking I expected a less well put together girl, but she has very good conformation for her breed.
I dont' think she is all that posty. Some, but her rear cannon is of a correct angle when placed with her hock (back of hock) lining up with the edge of her butt. Straight legs, a wee bit posty, but bones nice and straigt. Both rear and front canons are short, with rear higher than front (good). Her bone is very good overall, pastern length and angle is very good. There is a slight offset of the front canon (look at front view, it looks like the canon bone is offset to the outside , when viewed as a line straigt down from the middle of the upper arm bone down through knee to the pastern) But this is really minimal and I might not be seeing it so well, Because the grass, as a background for the photo, makes it hard to clearly see outlines.
Her back is good, pelvic angle very good. Neck lenght good and ties into shoulder good. Her head isn't as gorgeous as some but I bet when she sheds out she will look better.
All around, she is very well put together. If her feet are small (again, hard for me to see that ), that isn't an issue IF they are good and hard. I rode this paint filly a few years ago who had pony feet, but she was strong as could be and iron hard feet, though she did do better in shoes.
Love your filly.!~