Once again, MK, you are insinuating that a word allowed in Chihuahua is not a real English word at all. The cheek!
I suppose next you'll be saying that
boudoir is not an English word. Well what about
Milady's Boudoir, the magazine published for many years by Bertie Wooster's Aunt Dahlia, in the P G Wodehouse stories? Nobody could be more English than Aunt Dahlia, with her proud history on the hunting field.
Milady is to be found in many dictionaries. The online Oxford labels it as "historical, humorous", and says it is "Used to address or refer to an English noblewoman or great lady." As birdy indicates, it's sometimes found in historical fiction. An example of
miladies being used as a form of address is in
Clively Close: Wait for the Dark (1993) by Ann Crowleigh:
"Excuse me, miladies," Hopkins entered with Chuzzlewit in his arms, "Burton has walked the dog, mum."
An example of the word used to refer to people:
The servants left with the milords and miladies and such, and then I couldn't hear naught but the fire crackling before me.
- from
Lady Thief: A Scarlet Novel (2014) by A.C. Gaughen.
An instance of
milady being used humorously was in a 1999
Guardian headline, "Shotgun fury lands milady in prison", above an article about the resident of a Cornwall manor house who threatened two bailiffs who'd come about her husband's unpaid traffic fines.
Milord is already identified as rare, and I think
milady and
miladies should be the same in future.