I wonder if MT is just at that point of saying hell no, no more dresses. A lot of older women have made this choice and nowadays, with so many dressy pants-- make that trousers for you folks on the other side of the pond -- available, they have no desire and see no need to have to climb into all the dress-related underpinnings. Count me in that number, BTW.
I am sure she has a problem with aging and trousers are probably more comfortable. But you don't often see Queen Margarethe, Queen Sylvia, exQueen Beatrix , or Queen Camilla in trousers. And they all look good in their dresses, at least most of the times, plus they all are about 10 years older.
What strikes me recently is her grinning face in public, always that exaggerated smile as if she wants to tell the world how happy she is, that she is such a nice woman and all those bad rumours about her aren't true.