All this exposes is that she never read or heard ANYTHING on such an important event.

Agree, as I put in my comment. (I'm not at all trying to defend Haley whom I loathe.)

most of the secessionists put [slavery[ in their reason to leave the Union.

Cheers, didn't know this (my knowledge is patchy).

But doing a little bit of a search on the web I turned up this :

What led to the outbreak of the bloodiest conflict in the history of North America?

A common explanation is that the Civil War was fought over the moral issue of slavery.

In fact, it was the economics of slavery and political control of that system that was central to the conflict.

A key issue was states' rights.

The Southern states wanted to assert their authority over the federal government so they could abolish federal laws they didn't support, especially laws interfering with the South's right to keep slaves and take them wherever they wished.

Another factor was territorial expansion.

The South wished to take slavery into the western territories, while the North was committed to keeping them open to white labor alone.

Meanwhile, the newly formed Republican party, whose members were strongly opposed to the westward expansion of slavery into new states, was gaining prominence.

The election of a Republican, Abraham Lincoln, as President in 1860 sealed the deal. His victory, without a single Southern electoral vote, was a clear signal to the Southern states that they had lost all influence.

Feeling excluded from the political system, they turned to the only alternative they believed was left to them: secession, a political decision that led directly to war.

https://www.pbs.org/opb/historydetectives/feature/causes-of-the-civil-war/

My italics above. This seems to be in concordance with what I stated above - that it was more the economics of slavery rather than the morality of slavery that was the issue, and thus an issue of economic competition and state rights.

And I also turned up this :

The U.S. citizenship test – which immigrants must pass before becoming citizens of the United States – has this question: “Name one problem that led to the Civil War.” It lists three possible correct answers: “slavery,” “economic reasons” and “states’ rights.”

But as a historian and professor who studies slavery, Southern history and the American Civil War, I know there’s really only one correct answer: slavery.

https://theconversation.com/what-really-started-the-american-civil-war-205281

That author is arguing for the 'only correct answer' being slavery while noting that the citizenship test allows two other reasons - economics and state rights.

Looking around a bit more there does seem to be some contention about the causes. So like I also said in my top answer, it seems a complicated subject (not surprising for the causes of a war, which are often argued about and debated).