Ms. McDaniel is mistaken...

Ms. McDaniel is mistaken (though her mistake is unfortunately all too common in today's society); there is no category in United States law called "hate speech." What some people label "hate speech" is indeed protected as free speech in the United States.
Whether a purveyor of supposed hate speech should be given a platform by a private institution such as Princeton is a separate matter; Princeton is not legally obligated to do so. But before endorsing such private bans, people should consider what will happen when people who disagree with them are in charge of deciding which speech counts as beyond the pale.