She was in a hard place. If she hadn't given credit to the quote, the media would have blasted her. She could have named dropped a lot more, by saying, "In the words of my late mother in law, her late Majesty, Queen Elizabeth the Second..."
I mean, the easiest solution would have been to not use the quote at all, but it's a damn good quote. I think she rode the fence nicely.
It is a damn good quote. I lost a friend suddenly last year and I think of it often in reference to her.