Yeah, obviously stupid to do it in a way that could be tied back to you, but this is constitutionally protected speech.
The supreme court ruled in Virginia v Black that only “statements where the speaker means to communicate a serious expression of an intent to commit an act of unlawful violence to a particular individual or group of individuals.” are unlawful, and this doesn't communicate an intent to commit violence, just that someone should.
The supreme court has defined legally actionable threats extremely narrowly. Yeah that's a pretty direct threat, but I don't think it meets the legal standard of a "true threat"
In NAACP v. Claiborne Hardware Co. The Supreme Court ruled someone saying "If we catch any of you going into these racist stores, we're going to break your damn neck." was protected speech.
That's more direct than her threat.
There's an insanely high standard for convicting someone over a threat.