I think the white powdery stuff you are describing sounds more like exfoliating going on, which is normal, but, the smell is a red flag for you to address.
I found this site for you that helps explains what to look for and do.
Thrush is really hard to get rid of unless you are dedicated to getting rid of it.
From my understanding the over the counter stuff does kill it, but also kills the frog along with it which defeats the purpose.
I myself have been doing soaks with borax/water or lysol/water every other day or so and spraying with apple cider vinegar/water mix daily.
The acv/water spray mostly just maintains it after you have it gone, it doesn't really get rid of it, just keeps it at bay at most I would say.
Here is the article Horse Thrush - Signs, Symptoms and Treatment