No it isn't.
Besides, even if it were what they say it is, they have their terminology wrong. It would be libelous, not "slanderous". Slander is spoken and libel is written.
Should these sorry clownettes actually bring suit, Ann and her attorney(s?) will tear them a new one.
Might be fun to watch, if one was certain one had enough popcorn on hand.
But an absolute defense against a libel suit is truth and Coulter only tells it like it is.