I see a horse that is plodding around toe first on her front feet and not bending her hocks at all in the back end. She looks like an arthritic old horse that is trying to avoid bending her joints/moving them much and as a result, looks weak to me. Id be checking joints just to be sure. Have you tried putting her on an NSAID for a week and see if she improves at all? There are several things this could be.
I also believe that fitness is a big part of this. Is she in a small area all the time standing around or is she turned out over a larger variable terrain area with other horses making her move?
If this were my horse, id X ray joints if you haven't already to get a baseline, try a pain trial and turn this horse out in a large area where she will be made to move for a couple months and see if she improves. If she worked out of the bunny hopping, that says a strength issue to me, weakness that improved with work. I'm a big believer in turnout with a herd over varied terrain when there are odd soundness issues happening that cant be pinpointed despite the best care. Especially for a youngster.
After I tried those things, if there is no improvement, I would be looking at doing some in depth scanning if I really wanted to figure things out. Equine Chronicle » The Use of Bone Scan Nuclear Scintigraphy in Horses
She has always been turned out in a pasture where she can run with my other horse(s) since I've owned her, over a year now. Even the place she came from, which was horrible, except for the fact that she was turned out in a dry pasture with other mares. She has never been cooped up.
I am very hands on with my horses daily, always doing something with them. Even before she was started under saddle, I lead her around for walks or ponied her, did some light roundpen work. Now that she is under saddle, she is ridden almost everyday. LOTS of trails, sometimes for a couple hours on different terrain and hills etc. She is never in a stall. Her turnout area is 48 x 48 and then they have an attached grass pasture which is probably 48 x 96 and they are turned out daily....that is besides there walks and being ridden. My goal was to, exactly that, build strength and have her more balanced since she is green.
I did notice today, after turning her out and she ran off, later that she knicked her hind cannon bone. There was already a bump there on the bone from when she knicked it about a year ago, after I first got her. So she must hit it with maybe her other hind foot?
I really would like to take a video of her from behind while being walked up and down a hill etc and when she is turned out and running.....her fetlocks definately seem to lock up or something. I will work on that just so you guys can see how odd it is.
I did do the hopping test today and she hopped on both sides with me holding her front leg up. I also blindfolded her and walked her and she just followed me along like nothing was up....no drunken walking or anything either.
The chiro I have coming out I am hoping can really give me a good professional opinion and direction. I just want to start ruling some things out at least.
I have not tried any meds etc., really focusing on building up strength etc. No x-rays done yet since nobody really is sure on where to start.