I'm not sure McHugh's tweet is all that accurate, unless she was talking only about the London Bridge incident. I don't see how this tweet alone would result in a firing. Breitbart must have wanted her out for other reasons as well.
Far far far more egregious tweets, commentary, and blogs, have appeared on many main stream news media channels directed towards people of a "unprotected" class and the "reporter" faced very little to no punishment.