Ah, I think I've broken down a *real* brick wall this time.
My Dad had a Great Aunt he always called by a certain name. But in my research, I couldn't find this person. I found families with all the other names, but never hers. Very frustrating!
And then, just today, I was talking to him on the phone and he casually mentioned that this Great Aunt was a twin -- a very
important clue I was sort of mad he hadn't mentioned before.
In any case... one of the families I'd been zeroing in on did indeed have a set of twins -- but the birth name of one twin was correct, while the other was not (the "incorrect" should have corresponded to this particularly tricky Great Aunt).
So I checked the first census I could find that would account for her. And in it, she's listed under the "wrong" name.
I tried the next. Still the "wrong" name.
But the third census? A new name -- the one I'm looking for!
She must have decided to change her name in her late teens or early 20s. I don't know what the story behind that is -- and there's no one left to ask, really -- but this was definitely the lady I was looking for.