That goes for the pope as well. Both queen and pope are sovereigns and are immune from arrest. More than mere heads of state, each IS the state. Arresting either of them would be a serious violation of international law and would disrupt a whole raft of things.
So, maybe that would shock the world.
They would have to be arrested by their own people otherwise it would be a act of war. An egregious one! Although we DID do it in Panama, but I think in that case it was because their own people didn’t have the military ability to make the arrest.