APush is not easy, maybe easier than Euro but still difficult.
Have you or someone who is an English teacher (preferably elsewhere) ever looked at her writing? Is the English teacher correct? While the ACT writing is helpful, scores are too mixed up right now to rely but you are right that is quite decent.
Is he head of the department or does he have someone supervising him? Will D have him next year? Do you have younger children in the district?
Assuming she can write and this is the last time D or any member of your family will have him, I would find out from friends who are knowledgeable about how the district works what the best course is for appealing her grades or if it is possible. Obviously keep all her work.
Your best proof she can write is if she gets a 5 on English.
I would bring the Stanford quote I posted above to the attention of the administration. I personally do not think a higher AP grade is worth a lower class grade just because the teacher is strict. On the plus side, state colleges will usually give AP credit for a 3.
She can always retake. Since science was her worst score maybe try the SATs? Especially if she gets a 5 on English since comprehension questions are similar.