Yayyy, my pet peeve, founder/ laminitis/IR
First and foremost, if she's still ouchy on hard ground, her trim is definitely not right and she's not quite over the founder. Can you take pics of her feet? Loosie has a how-to link in her signature
Second, diet. Horses shouldn't go more than 4 hours without hay, or the stomach acids start eating away on the stomach lining=ulcers, plus, once they eat, insulin spikes, which you definitely want to avoid with a most likely insulin resistant horse like Misty. Has she ever been tested,btw?
Since Arabs are the poster child for IR( ask me how I know, lol), and she has foundered and was overweight, you can safely assume that she is.
My first action would be weighing the hay to about 20lbs, and divide, a smaller portion for the day, the larger for the night. I'd definitely ditch the RB for a better balanced mineral supplement more tailored towards IR, iron free, like California Trace, add flax, 2-4oz, salt, 10g magnesium and 2000IU vitamin E, in a carrier of a couple of handfuls rinsed-soaked-rinsed beet pulp. That should cover her mineral needs and give her everything she needs but didn't get because it's present in grass, but not hay.
I'd also soak her hay, 1 hour in cold or half an hour in hot water, it washes up to 30% of sugars and the excess iron out, which means less calories (less sugar =less calories).
Best thing about this diet is that any horse will do well on it, even if not IR, so her buddy can have the same, and should he need more to keep condition, you can add some rice bran or oil to his to get more calories. My three are on it, the little IR Arab, a QH and a TB, the two bigger ones get rice bran and less magnesium and are doing well.