How is it blatantly obvious from the character PoV?
Remember they dont see her evil face .. she's from far away, even if they look directly at her, the moon will silhoutte all the facial feature, and they should be more interest in reading witch's soul, which as stated, is camouflaged by her very well.
In short, just because we knew, doesnt mean the character in the story do as well.
And Nurse Medousa is the epitome of hawtness (even without showing any skins). PERIOD. In soul eater's world at least
