I mean... she's right.

And by explicit, he means explicit. They state their new nation is about slavery at least 4 separate times in a relatively short document, with black chattel slavery named as a requirement of any confederate state that was foundational, and could not at any point be outlawed. Their states had no “states rights” when it came to slavery.

The confederate States foundation was not a rejection of the US that happened to include legalizing slavery, it was was a rejection of the Union in order to forever legalize slavery specifically, as its primary aim, and they were not at any point shy about that fact in founding their slaver nation.