Sorry, I haven't seen this till now. It sounds from the news that you are getting into trouble with the hay supply in Texas these days. I'm sorry to hear that. I imagine there's a lot of horses to feed in Texas! I suspect that it is a lack of fiber/amount fed/nutrients that is causing her to eat manure.
Are any of the other horses eating something she's not? Corn will be "universal" like that. I don't think corn should even be in the diet. Very high starch content coupled with explosive energy. How's her weight holding? How many lbs. does she weigh and how many lbs. in those 3 flakes of hay is she eating? I'd take a weigh scale to the barn and actually weigh them, then see if they meet the 2% of her body weight that she requires. If not, then she's hungry for fiber and probably bored, cause she'll finish a flake in 30 minutes, then what about the other "xxx" hours of nothing? The slow feeders are called slow feeders and have smaller holes (1-1 1/4") vs. the normal hay nets. Way smaller holes. Make sure you got a slow feeder. a) considering the drought, these bags waste far less hay. b) will keep her busy longer in the stall and keep her stomach going longer. I saved $400 on my hay last winter for 3 horses. (that might make the BO sit up and take note) Ontario Dehy Timothy Balance cubes are a very good choice as a hay extender.
I also suspect that there is a lot of sugar in her diet. The Total Equine is not total to me, as I can't find a diet analysis of that product. (maybe you will be more successful) I don't like 35% NSC! I sure wouldn't feed that to laminitic or foundered horse, unless I wanted him to keep foundering. That number is very important and shouldn't be over 10-12% and sugar is not the answer to a drought situation. Horses need fiber, not sugar and balanced nutrients that will be absorbed. Starch is even worse than sugar and that's the baddie in the corn. Oats is worse. Oats is so high, that they use oats to measure everything else against it. What I would do is get a hay stretcher, not replacer. If she's not old and losing her teeth and ability to eat hay, I would lean on your best friend.....the hay, in a slow feeder. I would also weigh the hay and know she's getting what she needs. This is where she could lack for fiber. This might be also why she is still hungry and seeks out everybody else's "corn poops".
Another concern about the sugar is the pasture out there. I'm imagining that there's not much left of it. Once the grass gets into this kind of stress situation, the sugar has no blade to go up and work, so it stores at the base, tries to survive and wait for it. As the horse grazes on these nubs, its like pure sugar to him. Are there any dry lots available for exercise without sugar consumption?
Make sure she's getting her minerals. I prefer free choice, but if she's not eating them, then feed them and make her. (taste of copper is yucky) Buckeye, they eat like candy. There's no indication of flavouring on the analysis, but I know something is in there. If I free choice it, they eat more than they are expected to eat. (I'm quitting it, as new hay is in, have analyzed it and ordering minerals that are balanced with the hay. I just got it for the summer to carry me while waiting for the hay.) There's lots of good minerals out there, though and considering your drought situation, I would tend to get a good one in the face of it and put it in her stall. Don't mix salt in it. Keep it separate. 1-3tbn/day. Very important. Salt drives thirst. I'd probably be at 2-3 tbns./day in your situation. Water is everything when it comes to absorption, proper motility and metabolism, not to mention the electrolytes needed. Never underestimate the ability of trace minerals to boost her overall health/coat/feet. Magic stuff! If she won't eat the minerals, consider a flavouring. Herbalcom.com has red beet root powder, which they love better than carrots and will keep the sugar down in the process. Fennugeek is another one, but higher in sugar.
Another possible reason is that her hours of starvation with no hay has upset her enzymes and she's eating manure to get them back. She's "off" in her ability to absorb and metabolize. Foals will do this so that they can get the enzymes from Mom, so that they can start digesting what she eats. This is how they get their systems going. So, some probiotics may help also.
Whatever the reason that she is eating others poo, know that she is on a mission, lacking, and trying to make up for it.
I would address these areas;
1. Hay- make sure its adequate and lasts longer.
2. Minerals - if not eating free choice, feed it.
3. Salt and near the water or feed it.
4. Hay extender, which you can extend more as the needs arise.
5. Probiotics for a healthy gut.
6. Fresh ground flax 2-4oz/day....fights inflammation, beautiful coat and helps fight the sugar in the diet as well.
When you get things going, you may find that everyone is eating her poo instead. That should show the BO one heck of a hole in their feeding program. I hope things improve with the drought. Be watchful in the meantime. Consider that pasture not only useless, but bad as well. When they put the hay out there, does she eat it up immediately before starting to forage around? Or does she go out there and saunter back to the hay later? That will tell you something also. I would consider the pasture mere playground with the serious nutrition being served up at the barn.
You can buy a bag of feed with all this stuff in it, but they are also high in iron, which deletes the absorption of the minerals in it. If you mix the mineral/salt/flax/probiotics in daily baggies that the barn could feed for you. (a week in advance, for example) or free choicing what you can in the stall, you will be farther ahead and not adding more iron in the process. A handful of oats to deliver this meal won't hurt anything. Do what you can....what works. Also, if the pasture is just a mere playground out there, I'd consider her on a hay only diet as well. That means she needs Vit E.....1000mg/day. (3.... 400mg gel caps from the drug store) You could stick those in the baggies as well.
Another limitation to her diet is the fences around that pasture as well....hurts her variety needed. Bring an apple a day to keep the vet away, 2 large carrots have the daily requirement of carotene in its natural form. (vit A) You'd be surprised what all a horse can eat. Go for it. Don't overdo any one thing, but explore and see what she will eat, then add it. Nuts, seeds, fruits, veggies, grass from the other side of the fence, leaves off trees....anything. When you come to the barn it should be "salad time", lol! Mine are crazy for cucs! I actually grow a garden just for them, but grabbing a few things out of the fridge before you go works too.
Sorry, if I thought you were boarding, if you're not. Its all good anyway......
Hope this helps....