Bill, I hate to disillusion you, but that was no trumpet! It's a little known fact that Her Maj suffers from chronic flatulence (flatus catspawensis to give it its medical name), and spends much of the day trumpetting into her Damarts.
In her younger years, when society was less tolerant, the Royal Household would regularly appoint an official fart apologiser - usually a young and rather dim Army officer of middling rank - whose job it was to take the flak for the royal poots.
I say regularly because it was a job with limited prospects, and candidates weren't expected to last beyond the Season - often correspondence would reach the Palace to the effect: "It was lovely having Her Majesty to stay, but we must insist that she doesn't bring that flatulent, chinless oaf with her again..."
In these more enlightened times such flunkies are no longer needed, and Liz is "loud and proud", as that young prankster Edward would say. Her life has also been changed for the better by the grant of a Royal Warrant to the company which makes the renowned Viking Storm Gusset, which now features in all Royal togs.