I think your vet could have been more forthcoming? When something "pops & leaves a crater" that suggests it was a small infection of some kind, that happily ruptured outward & healed as best it could. Almost looks like the scale folded together & healed that way, & yes, I think you're stuck with that. But can't say what caused this in the first place. Very odd about the "upper lip swollen & edematous" too. Seems like she managed to dodge something pretty significant, & you may never know the whole story.