As I see it, "caught early enough" means that girl is cured but gone into debt and has to prostitute/is enslaved. Total turn into zombie is "too late".Honestly it's kinda weird how the game makes a point to mention that the zombification can be undone if it's caught early enough and you get items that supposedly would help do so but can never actually use them in that way.
And we can see "early enough" when protagonist dies - he gets bad status effect, but doesn't look like zombie yet and can cure himself with holy water.