I would go with Thrush buster, you can buy it off of valleyvet, and I would imagine most horse websites that sell items for horses. Its the top seller on valley vet, and I would use a syringe so you can really get the medicine down in the frog. Thrush is serious, its not the greatest thing that you didnt notice no offense... I would recommend picking out her hoofs more. Thrush has a really distinct odor that no one can miss. And most thrush treatments are really runny so a syringe will help with the mess too.
Hope this helps