c) The fact that this class just really is too difficult right now, she's missing middle school chemistry, and she needs to slow down?
This is AP Chemistry? Yes it is possible she has jumped too far. At my local H.S. AP Chemistry is only taken after a year of H.S. Chemistry. Has she taken regular H.S. Chemistry? Regular H.S. Biology? Algebra II? Chemistry requires a lot of math and if that isn't her strength it would be easy to struggle. Our school required co-current Algebra II or higher math for regular Chemistry, and a good grade at Algebra II for AP Chem. And the AP Chemistry class assumes that you have prior knowledge of Chemistry and a H.S. Biology class. If you go to the AP site you will find this to be their recommendation. Also the AP Chemistry tests/program was completely overhauled last year and it's possible the teacher is still struggling with how to teach the new class.
"The AP Chemistry course is designed to be taken only after the successful completion of a first course in high school chemistry. " from:
http://media.collegeboard.com/digitalServices/pdf/ap/ap-chemistry-course-and-exam-description.pdf
