Awesome, thanks everyone! I got the Tribute Essential K today and we're starting to wean her onto it and off the sweet feed tomorrow, hoping to have her on 1lb/day of the Essential K alone within a week to 10 days

And of course the same amount of hay as she's been getting still.
Then I guess I'll just keep an eye on her weight and make sure that if it gets too low, she gets something more to supplement. Essential K is expensive but since it's so concentrated the serving for a horse Sandie's size/type is only 1lb so it ends up lasting a good amount of time...and from what I've heard, it's worth it because it's a high quality feed!
The rep for Tribute and the vet told me I shouldn't need to feed her a supplement on it because it provides 100% of the vites and minerals she needs, and I don't even need to feed her a separate hoof supplement anymore because the biotin amount (and other things) in Essential K is just as good!
So YAY for feeding 1 thing and getting all 3 combined!

I just hope she likes it! Haha