CBS settled because a corrupt Trump administration could have cost them far more through acts of revenge. Settling was the cost of doing business. AOC doesn’t have any business interests a hostile, weaponised government could harm, so unless the legal system has been corrupted to the point where the government could charge her with libel (or treason or terrorism or anything else; at this point, there is no longer meaning, only power) because they say so, she has a solid defence.