Chasin the dream- You said she gets 2/3 scoop a day, why don't you cut that back to 1/3. That way she still gets the proper vitamins, and you don't have to add all those suppliments like I have to do at the ranch.. Some of the 39 horses that I feed get: SuperVite, CloeVite, Fast-track, Lysien, wormer, amplify, bute, and some oils... lol it can be crazy sometimes..
Be aware that if you are about to hit winter then your horse is going to stop gainin weight. So aslong as she gots hay, water, and grain then she will lose weight magically with no exercise lol
. Let the crazy ol' man winter shed some of her weight off for you.