So on my dial up connection the video was totally useless. However, head bobbing is usually more ass. With the front, than the rear. Horses only show what hurts most, so if she is a tad stiff in the back end, that doesn't mean she's not having some front end troubles. But, not being to see the video, I'm just speculating here. Also, you said she doesn't mind picking up the hinds, but does the front. They don't like shifting weight onto sore legs, and while they shift front/back, the also shift to the side, so a bad fore foot will cause the other fore to be difficult to pick up. Check for swellings in the fetlock area. Unusual lumps there indicate sesamoid injury/arthrosis. Bad shoulders, navicular, etc can all cause head bobbing. I'd look to the front. Bad hind ends tend to cause more subtle lameness, like a hip that drops quicker, or a leg lingers extended longer in the stride or snaps forward quicker. Head bobbing is usually to pull the weight off the hurtful foreleg. Look to see what moment in stride she's gimping (bobbing) when the heel hits, (if she lands heel first, that is-if not, that's a good place to look-the back of the hoof) or if she's really bobbing as she breaks over the toe (tendong pain, from long toes, or abscesss/bruise/thin sole at toe).