Read a little further; she has a point. I haven't digested it all, so I haven't made a conclusion. I'll probably go back to Farrand and give it a look.
I've engaged her before on the subject. She plainly ignores anything that contracts her views (which is very nearly any piece of scholarship on the Constitution), including the Federalist Papers and the constitution itself. It is absurd.
Indeed, though, you are correct on another count: Madison notes in Federalist 42 that the point of the commerce clause was to create a free trade zone.