She didn't get fired for this tweet, dumb though it was. She got fired for a long history of saying and tweeting things that are completely incompatible with the brand image that Lucasfilm and Disney protect viciously. She already lost a spin off series because of her social media spoutings, she apparently wasn't smart enough to read the tea leaves.
That's exactly what the stated reason was for firing her, was this tweet.
What's completely incompatible with the brand image? Saying your preferred pronouns are bleep bloop? Why are you reaching to protect big daddy Disney when they're ideologically purging people except when said person happens to be unsympathetic in your eyes?
We've gone from thinking Colin Kaepernick has the right to protest at work, in front of a large in-person and televised audience to Gina Carano can't resort to Godwin's Law despite that being fashionable over the last half decade.
It's not about free speech, or market effects it never has been. Spew the "right" opinion or suffer the consequences.