Put her outside for turnout and just bring her in for feeding. When turned out, put her on free choice grass hay, timothy, or an alfalfa mixed hay (40% or less alfalfa).
Put her on a better quality feed, like Triple Crown's Lite or Low Starch. SafeChoice is really not a good feed. It's high in starch, which can cause negative behaviors (like the stall pacing due to too much energy/anxiety) and isn't a fixed formula.
Or, you can make your own feed using a good vitamin supplement like horsetech.com's High Point, Uckele's Equi-Base Grass, or SmartPak's SmartVite line. Mix that with 2-3 lbs (dry weight) of shredded beet pulp, 1 cup of flax meal, and a calming supplement. For her second feeding, repeat the beet pulp and flax meal. If she won't eat the beet pulp, add some alfalfa pellets or whole oats.
The last option would be to use a good ration balancer feed like Triple Crown's 32% Supplement, Buckeye's Gro-n-win, or Progressive's Grass Balancer. You only feed 1-2 lbs of these for full nutrition. For extra calories, add 2 cups of flax a day, beet pulp, whole oats, etc.
Getting your horse on a more natural diet that gives her more forage (hay) to eat all day long will help improve her mental and physical well being. If you cannot provide free choice hay, then use small mesh hay nets, and give her more turnout time.