Sorry, but this is complete bogus. AOC is NOT trying to limit anyone's freedom of speech.
As you yourself mention, "free speech" does have rational limitations. You can't literally say whatever you want without there being any consequences. AOC should be allowed to block anyone on Twitter who is threatening her. Threats are not protected speech under the 1st amendment.
And she should absolutely condemn Republicans for baselessly calling her a "domestic terrorist" and putting her in even greater danger. That is inexcusable, untrue, and in no way similar to her calling people out as racists. She is allowed to speak out against this appalling treatment.