And her stepsisters didn’t recognize her. Just like Clark Kent’s coworkers. Dress up a little differently, and you’ll fool everyone.
Though, personally, I think it’s completely believable that Superman could obscure his identity by changing his clothes and hairstyle and putting on glasses. Heck, I probably wouldn’t even recognize him twice in the same costume, if it weren’t for the fact that his costume is so blatantly noticeable. ‘Cause, see, he had a completely nondescript face, with no recognizable features at all. (The curl on his forehead doesn’t count, because he only had that when he was Superman, not when he was Clark. I’m telling you, he didn’t just change clothes in the phone booth, he did his HAIR in there too. And it totally worked, because that was his only identifying trait.)