I don't think that Her Majesty would much care about the monogram. She wears bracelets with monograms of someone else, so I do not imagine she would care about this piece, particulary insofar as most people wouldn't know or be able to read it.
I think that the answer is simply that it isn't to Her Majesty's taste.
--Previous Message-- : It's not a very decorative piece is it though, : whilst beautiful and fascinating in it's : historical importance, there'd be few : occasions that would warrant the wearing of : such a particularly select piece of : jewellery as a monogrammed brooch from a : long deceased foreign crowned head. : : : : --Previous Message-- : It is a very interesting brooch, and it : makes : a beautiful museum piece. But somehow, I : doubt the Queen would every wear another : ruler's monogram or tughra. I think she is : right about that. : : :