Oats may just be the problem.
NSC [Non-Structural Carbohydrates] is a fancy term for the starch & sugar content of a grain, ingredient, etc. When it comes to oats, the NSC is usually around 54%, most of that starch and only 5% sugars. Starch is needed to build muscle glycogen stores and provide the explosive energy needed during training and competitions. While oat starch is digested mostly in the foregut, so hindgut ulcers due to fermentation aren’t a high risk, it is still energy.
Only getting 2lbs a day may also be an issue. Oats aren’t a ‘complete feed’, meaning they don’t contain 100% of a horse’s daily vitamin and mineral requirements. Oats are high in protein, calories, fiber, carbohydrates, and contain quanitites of iron, phosphorus, potassium, magnesium and manganese. They are nearly deficet in Vitamin A, Vitamin D, Vitamin E, The Vitamin B group, and Calcium. This causes a number of problems to arise, though very simply put your horse could have deficiencies in more than one category.
The easiest way to correct this would be to add a quality vitamin & mineral supplement. Though if you’re experiencing hot or behavior issues, it might be best to reevaluate her oat diet. There is a type of grian called a ration balancers, which are concentrated pellets designed to be fed at 1-3lbs a day. This contains the horse’s daily recommendations of vitamins & minerals while still being low sugar and low starch. The best ration balancers would be Tribute Essential K or Triple Crown 30%. Purina Enrich and Nutrena Empower Balance are also ration balancers, but aren’t as good as Triple Crown or Tribute.
I hope this makes sense for you (: Oats are the best cereal grain for a horse, far better than corn or barley. Though if your equine is an easy keeper, seems hyper, and isn’t getting a vitamin & mineral supplement then it may be time for a change.