I would imagine that Mud Fever could go away seemingly "on it's own," if conditions were right (some kind of natural vitamin A increase - MF has been linked to low Vit A levels, or some kind of major immune system bump), that that seems sort of unlikely to me. But who knows!!
My mare used to have chronic Mud Fever due to low immune function (she has an auto-immune disease that was undiagnosed for years - once it was diagnosed and we began treating her with natural immune boosting "stuff," she hasn't had a case of Mud Fever since!) and my game plan was always to shave those legs down, keep them really clean and dry, shampoo them once a week with this stuff
, dry the legs thoroughly, then liberally spray this stuff
all over the skin+scabs on the affected legs, THEN, final step, I would cover each scab with this cream
. I'd use the cream twice a day but only use the spray after washing the legs and only shampoo the legs once a week (don't want to dry them out too much by washing them too often).
That worked really pretty well for my mare (I also had a goat get mud fever and this same regimen worked in about a week on her! haha).
Of course, once I got her immune issues under control, mud fever was a thing of the past but you know.
The other cause of Mud Fever is usually a Vitamin A deficiency. I'm not familiar with how people deal with it that way but there are many people on the forum who are "in the know" that way. In case she doesn't come along, I know 'Trinity' is someone who will know - might be worthwhile to pm her. :)
It's something to do with significantly increasing the Vit A the horse is getting via a dose of some kind of cattle Vitamin A supplement that really bags out the V.A....I don't know. haha
Good luck! Mud Fever can be frustrating!!