These animals have us trained alright... Our kitty just walks over to the door and starts clawing the carpet. Asking nicely gets him nowhere, I guess, if he ever did try, so he decided "If I go over here and be bad, she'll get up!"
How was pony last night? Her stall a mess again? Is she close to coming in heat? As everyone else said, the excess salt licking would make her drink more, and urinate more. From previous pic of Cyn that you posted, she is such a curious horse, and would need something to keep her occupied while stalled. We have some of these in the barn.
Also, they have fillers for toys, that the horse can lick.