What exactly are you doing to correct the problems you're having?
You train or untrain a horse every time you ride. Food for thought.
Glad you realize that . Be careful of Selenium over doses. If she's an easy keeper why not put her on a ration balancer? All the nutrients without the calories.
If you're so well versed on equine nutrition why did you copy and paste from this site? Rice Bran for Horses
There's nothing wrong with feeding rice bran for calories along with a good vitamin mineral supplement. There are more cost effective "additives" though.
I use it along with beetpulp and Ultium for my ulcer prone horse. Rice bran coats the stomach with fat...beetpulp is high in calcium(acid buffer) and helps aid in hindgut digestion.
I wasn't trying to lecture you, but please, don't assume I'm ignorant on equine nutrition. You posted a thread for help, so I'm trying to. This includes the
Horses diet and training regimen. Is she sore?