Dry and clean are key to the management of thrush. As much as bleach is an excellent bacterial weapon, and was a common and cheap go-to for thrush years ago, it has long been known that it also will destroy new flesh, thus it is not the best approach to chronic thrush and rarely used beyond an initial scrub and even that is rare now. As the bacteria is killed off, this will expose new, raw and clean flesh, the bleach will burn and irritate it, leaving it open to any bacteria still present, in other words, if not careful one can drive the thrush even deeper into the tissues by using bleach or any other caustic (mouthwashes and liniments). The more prevalent products today are, effectively, cow mastitis medications (farm supply stores), and/or athlete’s foot products combined with triple antibiotic ointments (local pharm), or a vet call. Take care to use only one hoofpick, the same one, on that hoof and clean it after EVERY use so to not transfer and perpetuate the issue. Soak a strip of bandage gauze with Vetrycin or something like it and “floss” the sulcus, medicating there as well. By all means, feel free to bleach any standing surfaces, just not the hoof itself.
Daily use of products such as ThrushBuster or Dura-sole will definitely dry out any surface you address. This might be why the small crack in her hoof persists tho the crack sounds like the result of a small wound years ago, at the coronary band. If so, it is just the way she grows. Maybe try a bit of vitamin E rubbed into the coronet band above the crack, see if that helps a bit..Be mindful of your/her trim schedule, be religious and consistent about it. Hydrate well from within, keep mud and wet footing off and out of her feet, consider something like Koppertox, a sealant for the sole, when she is rid of the thrush. Once cleared, treatment should be required only once a week or so, depending on the wet factour. Good luck with your mare, Heather B, thrush can be a bear to eliminate when it takes a deep hold.
Sure there's right and wrong but mostly there's just a whole lotta different.