I'm not sure she didn't do the assignment as defined. From the whole article:
Dever said "childless" had a less derogatory tone, to which Pompeo replied, "And I will probably use the word 'BARREN' it is my choice; I don’t like to be told what words I may and may not use, ever."
The argument appears to be over the tone of the work, which may be part of the overall grade but cannot be final say on what is, essentially, an opinion piece. (I know the prof said it wasn't, but I see no way to separate opinion from critique, especially in an esoteric area like film critiques).
Did I miss something specific on why you believe the student failed to perform the assignment as actually defined (as opposed to the desired result on part of the professor)?
Also from the article: "The professors attempted to explain to Pompeo that her assertions in her "critical and analytic paper" needed to be substantiated in accordance with academic standards. Otherwise, they remained opinions, and the assignment was not an opinion paper."
She said that she would continue to use the word "barren". Barren, when used for a womb, means incapable of bearing children. As the professors pointed out, that is not accurate without substantiation. Saying that homosexuality is "perverse" is her opinion. She's welcome to it and she no doubt believes it is accurate. But again it's an opinion in a paper that was supposed to be analytic.
Monica Pompeo is welcome to her opinions, and I don't think anyone was saying otherwise. But the assignment wasn't to give her opinions but to perform critical analysis backed up with supporting evidence. And she didn't.
All in all I think Pompeo was in the wrong class to begin with. And I think this is more a GPA issue than a free speech one.