Here is a pic of my weanling filly (aprox. 5 months here). She's standing not "quite" square, but this to me shows a reasonably straight weanling in front, and it appears to me (draw an imaginary line down from the point where the leg exits the shoulder and perpendicular to the ground. The center of her toe should still be within that line, for ideal/straight conformation.)
The point at which the leg deviates, be it knee, pastern, or even hoof, is where you will begin to see the issue of whether or not it is conformational.
No matter where it starts, corrective trimming can really be helpful especially when they're young, to encourage the joints to grow more straight, though I will say it may (and is likely to) require far more frequent trimming, it is WORTH It even if it's every two weeks, to be sure that filly ends up with the best conformation possible, as once they are approx. two years old, the window for changing those angles closes and you will be left with a maintenance issue of dealing with the deformity, if it is indeed such.
Sometimes these problems are caused by nutritional deficiencies, as well, and so another ally can be your vet. Get them to analyze your feed program as well as her condition, and see what they would suggest. I have seen young horses w/problems in their legs that ended up responding very well to some even slight nutritional changes.
Just throwing some ideas out there and trying to give you a photo of a horse where you might try taking a similar one for others to see and give opinions on.
Or maybe someone could come on and point out what I'm so inept at!
Liz M.