Well, I think that your response of questioning the teacher is maybe right- IF the whole class did indeed make low grades. I'd make sure to know that before making accusations. If the class as a whole did poorly, then you will have some solid ground to stand on.
Now, let me give you another perspective... I was really bothered by you saying that her whole future is ruined. I went to a very good private high school, and I was a B student. I felt as if there was an over-emphasis placed on grades. When I left high school, I went on to University, and had no problem making A's- in fact, I felt as if it was too easy. (that sounds braggy, but it's honest) I was so frustrated that such an emphasis had been put on GRADES in high school. The mantra was "If you don't make good grades in high school, you're going to FAIL in the real world. We're going easy on you."
This hit home again last year when I was looking at my sister's 12th grade biology book. It was at or above the level that we were using at University.
So- on the one hand, I'm very thankful for the high school education that allowed me to breeze thru classes at the University. (although I did choose a major that was hard for me) But on the other hand, I was angry that I stressed so much over school. But on the other hand, I'm still very thankful for my education.
Sorry to blather on about it- I just feel very strongly. And I tend to get incoherant when I feel strongly about something.
It's not a good combination.