Clearly, she is referring to the Union of the Crowns under King James in which the crowns of England, Scotland and Ireland were united under a single monarch but as to which each jurisdiction retained its own sovereignty -- in other words, she is making the subtle argument that this event was the genesis of the principle of federalism that was later memorialized in writing in our constitution.
In her view, it was not the mere writing down of the concept in the Constitution that was the important part, but rather its earlier implementation under the Union of the Crowns that gave birth to the architecture of our government.
You give her way too much credit.
And way too much intelligence.
I would guess that she’s never heard of the Union of the Crowns.