This is a horrible thing, which would get someone arrested if they did this to a Democrat President. However, I wouldn't take it too seriously. Kathy Griffin would set herself on fire and run naked through the Superbowl if she thought it would get her attention.
Griffin is a third rate, little known, "comedian", and her bread and butter is attention. That is why she did this. She may or may not 'hate Trump', but that is not the point. The real point was to get her name in the public dialogue. Now, she will 'apologize' just to keep the thing rolling for as long as she can.