I agree with the consensus here that you need to tell your kid (and yourself) that life isn’t always fair and accept the grade. I would push harder if it was a situation where an A was pushed down to a C, or where a scholarship was at issue (ex: you’re NMSF and getting a C can be deadly if you want to make finalist). I also agree that grading in English is subjective and it sounds like your kid’s work was graded, just not to your satisfaction. My older D had issues with one teacher freshman year who would claim papers had not been turned in and give you a zero. D learned to keep all her graded work until she saw it entered in the on line grade book. That way she could prove to the teacher that she had turned it in, the teacher had graded it, and the teacher had just forgotten to enter the grade.
My daughter’s AP Lit teacher didn’t post grades for an entire semester. The kids had a general idea of how they were doing and had one teacher/student conference each quarter, but the teacher taught the class like a college class. No hand holding.