That wasn't an obvious threat.
I think, and I have only rudimentary legal training, that what she did could qualify as 'incitement to violence against the President'. I don't think it could be made any more clear that by her 'joke', she was saying to the world that she wants President Trump to be brutally murdered. That was the whole point as I see it. That was the 'joke'.
And it was clearly a reference to ISIS. Whether she actually supports ISIS, and their methods of torture and execution is now in question. I don't think she does, but she is who started all of this. Now you have to wonder?
We shall have to wait and see what comes of this.