Mudpie is on Farrier's Formula Double Strength, and I am extremely happy with it! It's helped his historically very unhealthy hooves become extraordinarily more healthy! It is not, however, a "complete" or "multi-purpose" supplement. Instead, it's designed to target hoof health alone. :)
Providing loose salt is relatively easy, and I personally recommend himalayan salt. Mudpie loves it, and I know that he's always getting the salts/minerals he needs. I provide it free choice, along with a standard red mineral block that he almost never touches.
If you're worried about your horse's diet having gaps, you can look into a ration balancer, or try to pinpoint her needs. :)
The hills were bathed in moonlight, the shadows not so stark;
Silver light reflected off his brown hide as he held me in the dark
– I love you, Mudpie!