As a fellow writer, editor, and writing teacher, I have not only worn your shoes but worn them to a frazzle. Sometimes I challenged them; sometimes I left it alone.
Once my kids were in high school, I would proof their papers if they asked me to, and if the high school teachers in their AP classes made that kind of error, I first encouraged my kids to challenge the grade. If the teacher pushed back, I would send a friendly note just letting them know the kids had discussed their issue with me and had they considered .... and then would cite the specific rule in question. I personally found the AP high school English teachers the most defensive.
If your daughter is in a lower grade, depending on how much that one score affects her grade, I'd be tempted to simply make my daughter aware of the teacher's discrepancy so that she knew the particular rule appropriately. But I'd likely not make a big deal out of it unless it became a pattern. But that's me - it was usually just not worth putting the teacher on the defensive with half a year to go if it wasn't going to make a difference in my child's overall grade.
