In my experience, its necessary to treat thrush daily. Getting the trim right is a big part. Diet too, especially copper and zinc. Focus HF is a good supplement to help grow strong, thrush free hooves. If the trim is right and there’s adequate zinc and copper in the diet, the horse shouldn’t get thrush. Even in a wet environment.
My favorite treatments are No Thrush and White Lightning gel. Apply and either have the horse stand on dry, clean footing for an hour or so or put on hoof boots and turn her out. I wound up using boots for the stubborn thrush my mare had, since it was easier for me to do that.
I’d avoid stuff like thrush buster and bleach. Yes, they’ll kill the thrush…but they’ll also damage the healthy frog under the disease frog.
Would it be possible to change to footing in her dry lot? I used to have horrid mud in mine, until I switched to 3/8" pea gravel. After all we have 5 seasons here in Maine. Spring, Summer, Fall, Winter and Mud (that lovely transition between snowy frozen ground to wet thawed ground). Yes, its an additional expense for the BO…but a pea gravel dry lot doesn’t get rutted like a dirt/mud one and its prettier too. And most importantly, I feel that pea gravel is a healthier surface for the horse to be on.