I'm Convinced My Child's Teacher Has It Out for Her

What is the best way to handle a high school teacher who just seems to--no matter what my child does--view her as a B student? It's her French class, and the class has many exams that are subjective. For instance, rubrics for oral presentations and written work differentiates between A's and B's by work being "very organized" and "organized," or "often uses complex sentences" and just "uses complex sentences." My child asks for feedback on her work, and she's (noticeably to the teacher) making an effort in class. The feedback she gets is as elusive as the rubrics--not very detailed, and it's not clear how to do "more" of what the teacher describes, since my child is already doing it. My child has always been a straight-A student, and she's incredibly stressed by this class, which she's currently getting a B in.