To help her build her hind you can work with her on the ground (just in a halter) and have her back and side pass. Backing gets frustrating for practically every horse on the planet because its not instinctive and rarely if at all used in the wild, so I would start with a couple steps and praise her. If she backs willingly, then ask more from her. Again sidepassing is not instinctive, but will help build muscle, I would just start with the basics on that. (You said she was a former show mare, she may already have a lot of this from her basic training)
If you do any long lining, you can ask her to trot down a long side, turn on the forehand, trot back, turn on the forehand, etc. That will also help her build her hind muscles and help with self carriage.
If she already likes jumping, you can throw cavelletis or ground poles into the mix.
I know this isn't really what you were asking, but I think your original question was pretty much answered :)
As for her attention span, some horses are just like that. You said she was abused so I'm not sure if this would be the best choice, but carrying a whip or a lunge whip definitely helps with attention, you don't even have to lash it for my filly and she's all about doing her job (where as without it, she's the typical mind-wandering three year old). I'm not sure how she was abused so it may be a non issue, but you can reintroduce the whip as a good thing before actually using it for work. (Get a bag of treats, the first day just have her look at it, maybe smell it if she isn't petrified and praise her.. the next day the same thing, maybe touch her if she seems comfortable.. keeping touching her with the whip all over to desensitize her until she realizes that its not there to hurt her. With my filly it took about a week or so, but she was never abused.. Go at whatever pace is comfortable for her)
If the whip isn't an option, I would try a plastic bag or or paper bag you can use to shake a little and make noise.. I'm not sure how it'll pan out, she may just end up looking at the bag instead of paying attention. :P (I use a plastic bag attatched to the end of my lunge whip so it makes a little noise when I lash it) Maybe try lunging her with it first and have the bag behind her as you would a whip...
Otherwise talking to her/clucking/kissing is probably the best you can do, other than varying the routine. Maybe try doing only a couple jumps in a row with her, then some groundwork (like backing or sidepassing), change direction, jumps, groundwork, etc. So that she's not sure what's coming next. Varying the routine (yet keeping the fundamentals the same) is important in training, so they stay engaged mentally. (Just like some high schools rotate their schedules so a different class is first every morning, the same principle is applied there)
Good luck, she sounds like a very sweet mare, and sorry for the length.. I go off on tangents :)