I would initially begin with a routine.
I would start by tying in the same location (crossties, stall whatever). Then start picking out the left front, then left hind, then right hind, then right front (or whatever order you want…). Then curry. Then stiff brush. Then medium brush. Then soft brush. Or whatever your routine is. Same thing, every single time you work with her. Make what you do predictable. Horses, especially ones given a reason not to trust people, thrive on routine. That said, my horses have no real routine once they’re trained and don’t seem to have a problem with it. I just gradually phase out the doing the exact same thing every time.
I’d get a book like 101 Dressage exercises and use the low level stuff. There are a ton of walk and walk/trot exercises that are awesome for starting horses who need to be kept busy (ask me how I know this…it was invaluable in starting my Arab as a colt!). Some have ground poles, some are using a bunch of figures, some are doing a bajillion transitions. All are good for keeping a horse busy. The exercises won’t be executed perfectly in the beginning, but that’s not the point. Perfection will come with time, just do them in the beginning. The point is keeping her brain busy.
Longing isn’t necessarily a bad thing, just do it in a productive way. I’d put some loose side reins on her (the kind with elastic, not a donut…I’ve found most sensitive Arabs find the donut more startling) and encourage her to stretch into them. Do lots of walk/halt transitions. When she’s calm and okay with that, move to walk/trot/halt. ONLY when she has a brain at that level, add the canter in.
When you get on her, warm up in the same way. Have a routine. Walk this direction, walk that direction, trot this way and that way if she can keep her brain. Then school a few exercises. Then ‘cool off’ in the same way each time.
The point here is not to tire her out. You’re probably not going to be able to do that…my Arab will happily trot/canter a 25mi endurance ride three days in a row and still be raring to go a forth day… However, you can mentally engage her and get her thinking. A thinking horse isn’t hot and wired, jigging all over the place.
Also, she’s a rescue. So what. Quit making concessions for this. If you go into this with the mentality that you need to baby her and be careful with her, you’ll need to baby her and be careful with her. If you remain predictable and calm when working with her, she will trust you and chill out. If you DO find something that spooks/scares her, don’t avoid doing that thing. Just matter of factly, methodically do that thing/introduce that thing/make her work near that thing/whatever. I appreciate the horse with trust issues (I’ve worked with several and owned one). However, you can’t make excuses for them and tiptoe around their issues. The more matter of fact you are with them (I’m not suggesting being mean/callous/whatever), the better off they usually are. Just be a good leader. If you act like XYZ is no big deal, sooner or later XYZ is no big deal. However, if you tiptoe around XYZ because the horse acted scared of it, you’ll just reinforce that fear.
I’m not opposed to using food rewards for introduction to scary things. I’ve taught my Arab to accept any number of things using treats. He learned to tolerate pulling a cart eating 5lbs of carrots one day. He learned to tolerate my force dryer (I use it to dry my grooming clients dogs) because its great for a ‘dry bath’ of sorts. He looks clean after I blast all the dirt out of his coat! Its great for the 6mo where its too cold to bathe. He ate a few handfuls of treats while I introduced that to him. He’s learned that tolerating scary things I do generally results in treats…and that the scary thing probably isn’t that scary.
As for not standing halted quietly, here’s how I train a nice stand quietly. I use it as a reward. I don’t ask for it in the beginning of a workout once I’m in the saddle (I expect the horse to stand quietly for mounting, but once I ask them to walk off, we’re not going to stand around just for the fun of it). We’ll do an exercise or two and then I ask the horse to halt to give it a break. If it wants to stand there quietly, fantastic. We’ll do that for a minute or two. I will go back to work the second the horse starts getting fidgety. I’ll do another exercise or two. Then again, ask the horse to halt and give it a break. Rinse, lather repeat. Most of the time, I can get 15-20 seconds of a good, still halt before the horse starts fidgeting in the beginning. It gets longer as you do this over time.
Standing quietly is a physical and mental break/reward for the horse. If it doesn’t want to stand quietly, I don’t punish or fight, we just go back to work. My trained horses will stand indefinitely with the reins dropped to the buckle in pretty much any situation because they have learned that standing quietly when asked to do is a good plan because there’s probably more work ahead. I can go from running full tilt boogie across a field on my hunt horse to a check, halt, drop the reins to the buckle and he’ll relax and stand quietly almost instantly. There was no fighting or arguing about learning to stand still. Its just always been a reward for a job well done. At these rest breaks, I don’t nag, I don’t do anything. If the horse likes a scratch on the withers/shoulder I’ll do that (gelding loves it, mare hates it - only likes a verbal ‘good girl’), but otherwise I leave the horse alone, all pressure/attention off.
Like others mentioned, I just approached it (and everything else with this horse) totally matter of fact and systematically. I don’t do drama 