I disagree. She said what she wanted. She was not censored by the government. The First Amendment is about restrictions government places on speech, etc. As for Snoop Dog, there were people who were offended. What probably made his less offensive was the "clown" aspect of Trump standin.
As for the woman aspect, my personal belief is that if cannot be criticized because you are a woman (or you perceive that all criticism is because you are a woman), you really aren't interested in equality. You want special rights.
I don't know Kathy Griffin. But if she was a man, I believe I would have had the same reaction. And the Secret Service would have had the same reaction. They don't know her either. Their job is to protect the President, regardless of who he is, and to assess threats to determine if they are serious or not.
Kathy Griffin MAY have intended this as a joke. But once she released it to the world, the viewer determines what it is. Kathy Griffin may not have considered that others would not find it funny, not think it was joke, and be offended. That comes from living in a bubble.
But she still was able to say what she wanted to. That's free speech.