That is a battle already lost. All we can do is keep the old, proper forms in our own postings here, but cannot expect that the wider public will do so. We cannot stop the tide.
I don't know where it started, but the press is magnifying and perpetuating such errors, and we can be sure that that will not stop. Google "Lord Stanley Baldwin" or "Lord Max Beaverbrook" and you will see how widespread this new modern usage is, not only in blogs and other informal things, but in respected newspapers, journals and books.
And of course in many obituaries these days we find people such as "Lady Mary Smith", only to find that the lady is the wife of a knight or even a peer, and is not daughter of a duke, marquess or earl. I haven't noticed what most posters in this group do with such names, but when I post them I usually put the "Lady Mary" in quotation marks to show that it was not I who wrote the name that way.
Even government sources no longer bother to use the older forms. Here is one example: one can find "Lady Julie Sandwich" in an official government record here:
https://register-of-charities.charitycommission.gov.uk/en/charity-search/-/charity-details/1000142/trusteesSo there's not much use criticizing Lady Mone for this, especially when she's been involved in so many worse controversies recently.