'Clubbed' feet in horses basically just means high heels and is generally labled as such when it's unilateral, although horses can have both front feet 'clubbed'. Reasons for this can be farrier error or otherwise allowing heels to grow too high(many laminitic ponies for eg). It is commonly due to posture/grazing stance - horse stands with one foot more often forward & the one that's back becomes 'clubby'. It may be due to injury or heel tenderness - horse is unable or unwilling to weight that heel, so more toe wear & heels grow down. Or it can be duet to congenital or developmental conformational issues - I think rarely a true case of one leg shorter than the other, but genuinely shortened tendons possibly not so rare, especially considering DODs in performance horses grown up quicker than their tendons & muscles can adjust.
Because it's frequently a body issue, I believe it is not *generally* something that a farrier should just attempt to 'correct' with trimming, at least without serious consideration of cause & effect. Getting a bodyworker involved may treat body issues that are at the root of it.
My mare is sound, sometimes ouchie on uneven up rooted trails but she wears shoes & my farrier has set her up nicely. She team pens and works cow & has always been barefoot untill now. I think its just a flare & she has a little bigger foot than the other.
Without more info, I'd just advise that pads are used under her shoes, to protect her likely thin, flat toe sole, and 'frog support' wedges to give her recessed heel on that foot *comfortable* stimulation. The flare should be able to be managed with frequent trimming and keeping the toe wall relieved of undue pressure.
With regard to your attached picture, a club foot commonly looks like the middle pic, as I imagine yours does, because the extra pressure on the toe causes it to flare if not managed adequately.
Clue #1. The flare is at the toe, not on the sides.
Clue #2. After rasping down the outside of the hoof at the toe, use a hoof protractor to measure the angle of the hoof. An angle of more than 60 degrees indicates a possible club foot.
Flaring may be at the quarters too, but more commonly just at the toe, whereas the 'low' foot of a unilateral commonly goes 'splat' right the way around. There are other reasons & problems that may cause a foot to be so steep and there are also clubbed feet that have a lower angle, because the entire dorsal wall may be nice & straight, but rotated away from P3.
Clue #3. With the horse standing on a hard surface, compare the heels of the front feet. The heel on the club foot will be higher than the other foot.
Clue #4. The club foot will be narrower then the other foot and the frog will be smaller.
Yes to #3 if they're odd & horse hasn't got 2 equally clubbed feet. No one is perfectly symmetrical either, so it's a matter of degree and subjective as to when you may call it a 'club'. Yes to #4 generally.
Yes to #5, again if it's unilateral. Also they will stand or graze with the high foot back.