O'Donnell has a valid point. Strictly speaking, it's not in the Constitution at all, but in the Bill of Rights ... the first Ammendments
to the Constitution. Although, I don't think that's what her thoughts were. I'm sure her thoughts were that the Constitution's original intent was to prevent the state from mandating a state-authorized religion, as was the case in Europe, and was the reason for many of the immigrants to the new country...to escape the persecution against their differences of belief with the state churches. The wording of the ammendment is fairly clear:
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof
In other words Congress shall neither establish the religion, nor shall it prevent it. To put it another way, the original intent was to keep the government out of religion
it was NOT to keep religion out of government. In fact, it was only in recent years that the Supreme Court extended the original meaning to go both ways, that not only should the government stay out of religion, but that religion also stays out of government. Quite recently, as a matter of fact ... the principal decision was as recently as 1948 and, believe it or not, the motto "In God We Trust" was still adopted as the official motto of the United States after
that .... in 1956
!! And even today Congress opens the session with prayer. There's a disconnect here somewhere.
I think that instead of regarding O'Donnell as ignorant, it might be more apt to regard her as politically insensitive; not a particularly good character trait for a politician; but on the other hand, might be a desirable trait in a person whose word you wish to trust. Depends what kind of a person you want running the country for you, I guess.