This typo theory is espoused by John F. Grant in, "Shows of Mourning in the Text of Jane Austen's Persuasion," in Modern Philology, 1983.

I've always assumed it was Elizabeth wearing black ribbons, (because, well, that's what it says! ;-)) and that The Elliot Pride was the reason why. But, I think an argument can also be made that The Elliot Pride would cause them to not wear black ribbons. Mr. Elliot had, after all, been invited several times to Kellynch and royally dissed them. And then there's this:

"Mr. Elliot had attempted no apology, and shewn himself as unsolicitous of being longer noticed by the family, as Sir Walter considered him unworthy of it: all acquaintance between them had ceased."

Sir Walter considered him unworthy of even being noticed by the family - so why would Elizabeth be wearing black ribbons? Would not The Elliot Pride keep them from giving respect to the death of the "inferior" wife of an unacknowledged relation? Someone so (if I might be pardoned a cross-book quote) wholly unconnected with him?